Resident Evil
44 Achievements
1,000
25-30h
CQC FTW
Finish the game using only your knife (no lighter, Defensive Items, and stomping zombie heads).
30
0.68%
How to unlock the CQC FTW achievement in Resident Evil - Definitive Guide
You can still equip weapons you just cannot use them. I mention this because the "Once Again..." play through starts you equipped with a Rocket Launcher.
Chris is the way to go for this achievement. Jill is terrible with the knife and has a lot less vitality. Here are some of the key points to help you be successful with this achievement.
1. Do not pick up any defense items. If you do pick one up, immediately go into your inventory and unequip it. This way you do not use one if the event you are grabbed by a zombie.
2. Stay away from zombies on the floor. There are very few instances of this but one in particular that stands out is when playing as Chris, if you go down to the Kitchen during your first run through the mansion there will be a zombie lying unconscious on the floor. If you run past him he is likely to grab you and then you will most likely stomp his head and void the achievement. The Kitchen I'm referencing is at the opposite end of the long hallway where Kenneth is.
3. Speaking of the Kitchen, the only reason you would go to the Kitchen this early is to get one of the four "Old Keys" to progress. However you only need two of the four to progress. You can find one in the very first save room you find that contains the "Fuel Canteen".
Another one can be found by leaving this room and going up the adjacent stairs and into the door on the left. You will enter a small room with a door on the left and one of the right. The one on your character's left is locked (requiring an "Old Key" coincidentally enough) and the room on your character's right contains the second "Old Key."
The third can be found in the bathroom next to the door that leads out to the patio that has the "Chemical." I recommend getting the third one and using it on the gate in the cemetery that leads to the Stained Glass puzzle room. This is an amazing route that was not included in the original PlayStation version but added for REmake on the GCN. This route saves on time and allows you avoid the two real nasty Mansion ambush rooms throughout your run.
4. If you are doing this achievement on a "Once Again..." play through and have "Real Survivor" and "Invisible Enemy" modes unlocked then you will also have unlocked "One Dangerous Zombie" mode. This addition is activated automatically when playing "Once Again..." after it is unlocked and cannot be turned off. With this addition, Bravo Crew Omni man and Maintenance technician Forest Speyer (nice work on our helicopter Forest...) will be running around the mansion free and reanimated as a Crimson Head. The difference is he can follow you through rooms and is strapped with grenades. If you attack him in any way you will set off the equivalent of a tactical nuke and you will die. Every time. The way to avoid this is to avoid Forest. If he does grab you, just shake him off. You are unable to use defense items against him, nor should you have any. Upon reaching the Residence area, Forest will despawn and you can play the rest of the game worry free of him. I do not recommend playing on any of the special game modes for this achievement.
5. Avoid all unnecessary quests. Only go out of your way to get health items and even then you should weigh the risk and reward. You will end up with more health items than you can count by the time your done so don't stress about that.
6. LET RICHARD DIE!! Do not go get the serum when Rebecca asks you to. Let Richard die. This is critical and if you do save him you will make this much harder on yourself later. I'll explain in the bosses section.
7. When you return to the Mansion after the Residence you will eventually enter Spencer's study using the Emblem key. When you enter a cut scene will occur where you hear Rebecca scream. Unless you are going for a specific ending, just let the Hunter have his fun.
Enemies
Zombies. Just dodge. Even if they get you, Chris can take three bites before going into "Caution" status and health items shouldn't be an issue. Just remember risk versus reward. If you kill that zombie it will come back as a Crimson Head. Make sure if you do you are not returning to that area.
Dogs. You only HAVE to fight one - the one of the terrace with the collar. Just go toe to toe with it and it will die in 2-4 stabs. There is a potted plant nearby with three fixed herbs you can use. Other than that just avoid them.
Crimson Heads and Hunters. It's your funeral.
Spiders. Big and slow unless going on a straight line. Avoid and just run circles around them. Not worth getting poisoned.
Chimeras. I highly recommend killing the first one you encounter in the labs. It is in the first power room where your get the "Fuel Supply Capsule." I recommend this because when you return with the capsule with the nitro compound if you get hit too many times the capsule will explode and kill you. By this point you should have more first aid sprays than kills so have at it. It should die in 4-6 stabs.
Bosses
Most battles can be avoided. When I got this achievement I only killed 20 something enemies. Don't engage unless you have to.
Yawn 1. Just run to the back, grab the mask and get out.
If Yawn manages to bite you, you will be poisoned and upon leaving the room, Rebecca will tasked with getting you serum. Doing so will net you the achievement for saving Chris as Rebecca.
Crimson Head Prototype 1. This is the boss you will fight in the crypt after placing the four death masks. This is the toughest fight for the knife only run through. My recommendation is that when Rebecca is in the piano room practicing Moonlight Sonata, you should get the other three masks from your inventory and place them in the crypt. This will free up room for some health items. During the fight you will want to run circles around him and pick your opportunity to strike. He is very fast so you will end up just trading stabs with him most of the time. An important note is that Crimson Heads most often attack with their right hands (sorry lefties, even in death you get no love). Try to favor his left side while you circle him to avoid his attacks. You will still most likely take some damage and he does have the ability to attack with his left hand so don’t solely rely on that to save you.
Mama Neptune. When you enter the Aqua Ring you will get a sight of Mama Neptune and her two pups. Go to your character’s left and into the control room. When you go down the ladder you will see the control room. Face the pane of glass that is on the right of the entrance. This is where the water drainage system is located. Activate it. Mama will ram the glass and you will be on a time crunch to get the water drained before she bashes it in. Facing the console you were just on, look to your character’s right and release the safety. Now turn around and the use the console opposite of you to activate the shudders (to your character’s left as you were facing the glass MN rammed). This will not work and you will have to manipulate the oil valves. Go to the back hallway and activate each valve until you get the right one. It is random each time. The solution is on your character’s left as they enter the console room on a desk near the map on the wall. Release the safety again. It is the console on your character’s right as they are facing the MN glass. Then turn around and activate the shudders again. Finally, face the MN glass and activate the drainage system. No go out the door and through the rusted double doors to your right. Go all the way around and find Mama Neptune. Go up and try to grab the key, she snaps, you push the generator in the water, pull the lever and she gets cooked.
Plant 42. This is why we let Richard Die. Richard clearly isn’t that bright and has a tendency to find himself in the jaws of large animals so who cares. If you allow Richard to die from poison you will be tasked as Rebecca to create a plant killer to kill plant 42. If you save Richard you will have to fight Plant 42 as Chris. Since this is a knife only run, we don't want to fight Plant 42 as Chris but gas it to death as Rebecca.
You will find a report titled “Plant 42 Report” in room 002. This is the same room with the ladder down to the Aqua Ring. Some people say this is required to activate the Rebecca side quest and some people argue it is not. I recommend grabbing it anyway since you will run right past it on more than one occasion. When you enter the Plant 42 room a cut scene will occur and Rebecca will barge into the room. Chris will throw her the book to make the V-Jolt and you will take over as Rebecca. Immediately unequip your pistol! We don’t want any accidental/negligent discharges. Go over to the room on the right with the electronic lock. The combination can be found in the break room by looking at the pool balls and checking the corresponding color and symbol of the oil lamps located throughout the room. However that would mean more time with the two giant spiders so just keep putting in different permutations of 3, 5 and 6.
Once you are in the room go ahead and pick up three of the bottles. You will notice the solution to this puzzle has been scrawled into the wall next to the door. We have to use the two chemicals and water to make the V-Jolt, or UMB-20. Each of the chemicals and water has a number.
Water – 1
Red – 3
Yellow – 6
There are numerous ways we can make a sum of 20 with these numbers but going out of order will create toxic fumes so let’s do it the prescribed way.
1. Fill a bottle with Red (3)
2. Fill a bottle with Water (1)
3. Combine Red (3) and Water (1) to create Purple (4)
4. Fill a bottle with Yellow (6)
5. Mix Purple (4) with Yellow (6) to create Orange (10)
6. Fill a bottle with Yellow (6)
7. Fill a bottle with Water (1)
8. Combine the Yellow (6) and the Water (1) to create Green (7)
9. Combine Green (7) and Orange (10) to get Blue (17)
10. Fill a bottle with Red (3)
11. Combine Red (3) with (17) to get Brown (20)
12. You now have UMB-20, also known as the V-Jolt
Now take the V-Jolt to the Aqua Ring. Since the water is drained you will have to go all the way around and back up through the control room. Then head to the back of the ring where the guard room is. Enter and use the V-Jolt. Plant 42 will wither and you will resume control of Chris. However Plant 42 is not finished yet. At this point you will have to stand underneath it and swing your knife in the air at Plant 42’s tentacles. Keep moving and slashing at the air when the tentacles are hanging down. Don't stay in one place too long. Take a few swings and run a circle. Sometimes you will think you miss and not see any blood. When I defeated it I was swinging at air so just because you don’t see blood doesn’t mean you are not doing damage.
Note: This method will also net you the achievement for rescuing Chris as Rebecca.
Black Tiger. This is the extra large spider you encounter in the caves. She is going to rush you right off the bat so run left or right as soon as you take control. Run to the door and start slashing. Six slashes and you can go through the door. There are blue herbs on the other side in case you get poisoned. Sometimes this googley eyed beast won’t turn around and come after you and other times her spidey sense goes off and she gets you before you can finish the door. Run her in circles or keep slashing at the door, either way will work. You will have to return to this room for the trek back to the elevator room. BT and her two minions will still be present when you do. Just sprint to the opposite door. She shouldn't bother you because she will either not see you or let out a call to her boys that you are back. By that time you should be long gone.
Yawn 2. See the bookcase? That’s right. Keep running him in circles around the bookcase and stab his tail. Just be patient and don't get in a hurry. The only real way you can lose this fight is if you get impatient and take too many risks. Now if you do decide you want to play aggressive, keep him in the open area and wait until he strikes and move out of the way. The timing is really easy once you see it a time or two. When he misses (hell even when he hits for that matter) he is incredibly slow to reset and get back on target so you can get in 3-4 stabs while he does that. Take him back through the bookcase to reset so to speak if you need a breather. He can’t poison you in this battle so don’t worry about that. I still recommend bringing 3 RG herbs or first aid sprays just in case. No reason not to since you just be overflowing with them.
Lisa Trevor. Nothing different here. Push the stones and let Wesker do the work.
Tyrant. This guy does not live up to the hype. Run around his off claw hand and stab him. He may quick turn on you here and there but for the most part this guy is a complete joke. You should have 5 first aid sprays in your inventory just because there is no reason not to. Don’t be surprised if you end up not using any.
Tyrant 2. Since we did not save Rebecca or Jill this fight doesn’t take place. Fire off the Signal Rockets and hitch a ride with that pathetic excuse of a teammate Brad (you’ll get yours you worthless piece of dog shit…) and get out of there.
Congratulations!!
You just beat Resident Evil using only the knife. The achievement will pop at the summary screen that shows your time, ammo used (should be 000), creatures dispatched and health items used.
Questions, Comments, Concerns or Feedback? Let me know if there is any way to improve this solution.
This video was posted for another guide but if you're going for knife only you can follow it too as the dude breezes through the game with it. I also managed to get 3 of the other hardest achievements (beat game under 3 hours, beat game under 5 hours, and beat without saving) as well thanks to this video.
Again, all video credit goes to Shin Arko Phoenix
The final rocket launcher does NOT effect this. I used it and the achievement unlocked. the final ammo count was 0 even though I used it twice.
For Yawn simply knife it's tail over and over. The hunter that attacks Rebecca goes down pretty fast, just be careful of it's instant kill charge up attack. The Crimson Head Prototype can be a bit tricky as it's very fast so bring a few herbs. And Tyrant is surprisingly easy if you hit it once then run and repeat that pattern over and over.
Electrifying the giant Neptune shark doesn't count as it's a puzzle and using the rocket launcher on Tyrant doesn't count either so don't worry. Just be careful not to burn any zombies or use defensive items. Set defensive items to manual in the options. I'm not sure if the zombie in the tub that Jill crushes automatically counts so best to avoid that one just in case.
In order to unlock this achievement, you have to beat the game using only your knife. It can be done using any difficulty with either character. Chris has a better knife, does more damage with it, and has more health, but Jill is able to skip the Plant 42 boss fight completely. If you start with a handgun/rocket launcher, unequip it and deposit it in an item box as soon as possible.
I did this playing as Jill on Very Easy mode.
Notes
Along with the obvious (firearms), you CANNOT use:
- Defense items. Avoid picking them up. If you do pick one up, go into the options menu and make sure your defense item use mode is set to "Manual".
- Kerosene. This means no burning zombie corpses.
- The zombie head stomp. Playing on Very Easy, I never encountered a crawling zombie.
You CAN use:
- The herbicide against the fountain plant in the mansion's greenhouse.
- The water flow control system unit against Neptune.
- The insecticide against the bee nest in the guardhouse residence.
- The bee squish. Stepping on any bees that are on the floor will not void the achievement.
- V-JOLT against Plant 42. If you're playing as Jill, this will let you skip the Plant 42 boss fight. If you're playing as Chris, you still have to fight Plant 42, but it will start at half health. Also, as Chris, in order to use the V-JOLT, you have to let Richard die by not getting him the serum.
- The rocket launcher against the 2nd Tyrant battle on the helipad. I recommend letting Barry (if you're playing as Jill)/Rebecca (if you're playing as Chris) die earlier on so you can skip the helipad battle completely.
Enemies
You only need to kill one non-boss enemy (well, just one with the knife), and that is the collar wearing Cerberus (dog) on the mansion's outside balcony. Dodge when it leaps at you, then slash downwards at it while it recovers. If you take any damage, there are green herbs in a plant trough. You can't take them with you, but you can heal three times using them. Technically, you do kill bees when you use the insecticide on the nest in the guardhouse. All other non-boss enemies, and even a few bosses can be dodged/skipped/avoided.
Bosses
Yawn (1st encounter in the attic) - Simply run to the back of the attic, grab the death mask, and run back out. Yawn is very slow, so you should be able to grab the mask and get out without getting hit.
Crimson Head Prototype 1 - For me, this was the most difficult boss battle. Wait for the Crimson Head to lunge at you. As soon as it does, run behind him and slash. Run away from him and repeat.
Lisa Trevor (1st encounter in the cabin) - Lisa is invulnerable, so your only option is to run. Try to lure her to attack, then run by her while she recovers.
Neptune - Push the water flow control system unit into the water, then flip the lever.
Plant 42 - If you're playing as Jill and you use the V-JOLT, you won't have to fight Plant 42 at all. If you're playing as Chris and you use the V-JOLT, you will still have to fight it, but it will have half health. Use the stairs and the walkway and slash at the tentacles.
Yawn (2nd encounter in the library) - Climb down the ladder and go to the narrow area behind the bookshelf. Wait for Yawn to come close, then run away and go around the bookshelf until you catch up to its tail. Slash at its tail. You should be able to get two slashes in per lap.
Black Tiger - Lure the Black Tiger away from the door covered in webs. Use your knife to clear the webs and go through the door. You may get hit a few times. There is a green herb and two blue herbs on the other side of the webbed door in case you get injured and/or poisoned.
Lisa Trevor (2nd encounter in the winding underground passage) - Same strategy as the 1st encounter, just run. There are two paths. Lisa will appear in the first path you go down. Start going down one path, wait for her to appear, then turn around and take the other path. This way you won't have to try dodge her by running by her.
Lisa Trevor (3rd encounter in Jessica's tomb) - If you are playing as Jill, you have the option to give Barry back his gun. I recommend NOT giving him back his gun. This will allow you to skip the 2nd Tyrant boss fight later on. As Chris or Jill, simply dodge Lisa and push the stones off of the ledge. If you get too far away from her, she will jump over the coffin in the middle right towards you. As soon as she starts jumping, run away from that spot to one of the other stones. You'll have some extra time to push a stone or two before she catches up to you. If she does hit you, there is a chance she will knock you right off the ledge.
Tyrant (1st encounter in the labs) - Run behind Tyrant, and slash at his backside until he turns around. You should be able to get two slashes in before running around him again. He isn't very aggressive, and didn't try to hit me once while I was running by him.
Tyrant (2nd encounter on the helipad) - This is the boss fight that can be skipped if you let Barry/Rebecca die earlier in the game. If you did save them, you'll have to run around until Brad drops the rocket launcher from the helicopter. Tyrant is much more aggressive this time around. He moves much faster and has quite a bit of range with his claws. He will attack Barry/Rebecca, which will take up a lot of time, but will likely kill them in the process. If that does happen, keep your distance from Tyrant until the rocket launcher drops.
Summary
There are only five monsters in the entire game that you need to kill using the knife: the collar wearing Cerberus, Crimson Head Prototype 1, Plant 42 (optional as Jill; required as Chris), Yawn (2nd encounter), and Tyrant (1st encounter). Every other monster can be dodged/skipped/avoided or defeated with the environment
If you have any questions, please let me know.
(Missable) This is one of the two most difficult trophies, but unlike the other this can be made easier by playing on Very Easy difficulty. As it says, you can’t burn bodies, use defensive items, or stomp crawling zombies; the one exception to this is using the Rocket Launcher to defeat the Tyrant on the Helipad, though this is only applicable if you’ve saved Rebecca or Barry. However, it is important to note that should you use the Rocket Launcher and miss, this can void the trophy, so if you chose to save the characters be aware of this as it can potentially mess up your run. Because of this, it is best to just power through the game and avoid saving anyone, which leads to no battle with the Tyrant on the Helipad whatsoever. Since all other weapons are not allowed we strongly advise using Chris as he’s capable of taking more damage than Jill which gives him a better chance at survival.
See Gameplay Helps/Hints for additional details.
SPECIAL NOTE: If you're starting from "Once Again.." and have the Infinite Rocket Launcher unlocked, your knife will have been moved to an item box. Simply unequip the IRL and progress through the game avoiding enemies until you can drop it off and switch for the knife.
Secondary Note: If you have unlocked "One Dangerous Zombie" and you don't want to deal with Forest (the zombie), boot the game fresh so you have the original title screen and select new game. Select the bottom answer in regards to "walking" to be on very easy. If you don't care about Forest, simply DO NOT ATTACK HIM and shake him off if he grabs you. That's all there is to it, one swipe from your knife and you'll blow up.
As the achievement description states, you cannot burn zombie bodies or crush their heads. In addition, no daggers/stun gun/flash bang grenade. You'll want to do a few things first:
- So what you'll want to do first is go into your Options and select "Controls", then switch "Defense Items" to "Manual". This means even if you accidentally pick up a defense Item, you won't use it UNLESS you press .
- The second thing you should do is set the game to "very easy." If you're starting the game fresh from booting, it'll have the darker eye-title screen instead of the once again green eye. Basically, if you want to approach it like this, select the question that answers with "walking" (this will be very easy).
- You want to completely avoid the Canteen. There's no reason to pick it up but if you must, move it immediately into the Item Box in the same room.
- As far as I'm aware, there's only one Crawling Zombie in this game that you need to worry about and that's in the kitchen. If you're playing as Jill, you don't even have to enter the Kitchen until the second half of the game and that zombie will be gone by then. On very easy as Chris, I don't think the zombie is even in this room so you should be fine. On the rare occurrence you end up with a zombie who decides to crawl, DO NOT LET IT GRAB YOUR LEGS! If you crush its head you need to reload an old save because that will negate the achievement.
- USE V-JOLT! If playing as Jill, this means you never have to fight Plant 42. The kill from Barry won't negate the achievement. And as Chris, this weakens the plant to 50% full health which will make things easier on you! If you're playing as Chris, make sure to LET RICHARD DIE FROM THE POISON! Basically when you come across Rebecca, chill for five minutes outside and then come back in, he should be dead. Now when you go to fight Plant 42, you'll get a scene where Chris is grabbed and you'll be playing as Rebecca. She can go make V-Jolt and use it on the roots but you'll have to finish the fight (sorry Chris, no Barry to the rescue)!
I recommend doing this as Chris, because he has more health (up to three bites before he'll enter caution). You can go for either ending, as using the Rocket Launcher at the end to beat the final boss will NOT negate this achievement. In addition, it is probable that the zombie head-stomp that Jill performs in the bathroom cut scene in the mansion WON'T negate the achievement though it's not recommended to even enter that bathroom as you won't be using Defense Items anyways.
While the achievement sounds daunting, all you need to do is play on Very Easy and utilize zombie-dodging techniques used in your speed run. You really don't want to fight any of the regular enemies, it's a waste of your time and puts more risk to you than simply running passed everything. You barely have to swing the knife, just at a few bosses. There's more than enough healing items to keep you alive, but if you need, save often. With this in mind, you only need to deal with a few enemies outside of bosses:
- Cerberus with the dog collar. As soon as you blow the whistle, let it charge at you. Because of its unpredictability, it may leap or it may just try to bite from the ground. Whatever the case, get around it and start stabbing down. It won't take many swipes (3-5 I believe) to kill it. If you wish, you can just stand at the doorway and keep swiping until it's dead. As for the other Cerberus, I recommend avoiding it completely.
- Zombie in 002 of Residence. I'm only listing this zombie because you don't actually have to kill him, you can wait in the bathroom and he'll eventually open the door. Just run passed him when he does this and you'll be home free. Alternatively, you can let him grab you for one bite then push him off. Kill him if you want but it's unnecessary.
- Glasses zombie in labs. When you reach the labs, you'll go down a set of stairs to a gate. To the left of your character (right based on the camera angle) is a enclosed hallway with a zombie walking towards you. Deal with this zombie whenever you wish but make sure he's dead, as you don't want to risk the bite causing an explosion later on (when you're carrying the Fuel Capsule). You can make a save and risk it if you wish, it's up to you. As long as you move fast he shouldn't come back as a Crimson in time.
- Chimera in the first part of the power room. This is where you'll be getting the Empty Fuel Capsule and placing the full one. On the path to the capsule there is one Chimera who will always be there on all difficulties, simply kill this Chimera (slash down at it and avoid being grabbed if it's hanging) and ignore all the others in the room.
Finally the main problem with this achievement: the Bosses. They're really not all that much of a pain and even a newcomer to knife-runs can complete the battles. My top recommendation? Save before each fight and go into all with an inventory full of full-heal items (3X Green Herbs/Red+Green Herb/First Aid Spray)! Alright, here we go:
- Yawn 1 - In this fight, you literally are not fighting the Snake. Run as fast as you can to the Death Mask in the top-left corner, grab it and book it out. Try not to get poisoned on your way out.
- Crimson Elder - There are two ways to approach this sucker. Learn how to dodge his attacks and look for openings, which can turn this battle into a real lengthy one if you're trying to avoid getting hit. The easier method? If you're playing as Chris, use all four of the Death Masks then run back up the stairs to fill up on five full heal items plus the knife. Now head back down and get the battle started. Just stand where you are and constantly knife him, doesn't matter if he slashes or grabs, shake him off and keep swiping. He'll eventually go down.
- Plant 42 - It's recommended to stay in motion but, I don't know, I just sort of stood at the base level and kept swiping up at the tentacles. You'll notice less as the battle is ongoing and eventually it will be dead. Recommend using the Red Book to get the door open, then going back for full health items and saving. Also, as mentioned at the top of this solution, USE V-JOLT! If Chris, also check that section as it will mention how to get it.
- Yawn 2 - Yawn is a matter of patience. You CAN get out of this without a scratch but having health items on you is still a great benefit. Once you're in the main library area, go behind the book-shelf where you'll receive the blue book and constantly lure the snake back here. Once you see it coming from either side, run out into the open and go to where you see the tail and follow it, taking opportunities to swipe at it. You might get 2-3 swipes at a time but keep this up and the Snake will eventually die. Alternatively, you can wait back there and get hit by Yawn allowing yourself to possibly get stuck between the wall and its body allowing you to swipe multiple times (5-6, maybe more).
- Black Tiger - Don't even fight the spider! As soon as the fight begins, run towards the webs and start swiping away with the knife. Chances are the spider will try to charge you at the beginning of the battle (he doesn't always do this) so if he does, just check your health after and heal when necessary. If you get poisoned, there's a blue herb in the next area.
- Lisa Trevor - Obviously no fighting here on any occasion, the knife does no good. Just run. In the Altar fight, it's mainly about luck watching where she is and hoping she doesn't knock you in the pit. You can try to lure her but...even that's risky. If you're Jill, Barry's Magnum will do severe stopping power against her, might even knock her off the ledge (to her death? Very lucky if you get that but probably just hanging there). If it's Wesker (because you're playing as Chris), she'll focus on him for a bit allowing you time to push the stones. If Wesker "dies", he will still be in the lab later.
- Tyrant 1 - The fight in the labs. Like with the Crimson Elder, this can involve running around the Goliath and stabbing at opportune times. You could just stand there and swipe at him until he falls unconscious. It took me less health items fighting him than it did the Crimson Elder.
- Tyrant 2 - This only applies if you saved Rebecca as Chris and Barry didn't die during the Lisa Trevor fight. What you want to do is get to the roof and NOT DO ANYTHING until the timer is at 30 seconds remaining. Then fire the signal rocket and Brad will throw down the Rocket Launcher. Use it and destroy the Tyrant!
I hope these tips helped you out, the achievement isn't too difficult and some have even combined it with Invisible Enemy. If you decide to go that route, remember where enemy positions are and pretty much do the same thing mentioned above for each boss, but preferred if you don't go for the best ending.