Sunset Overdrive

You must accumulate 325 Chaos in the 3 mini missions before the night defense portion, then also complete the night defense without failing.

This partially luck but when the voting screen comes up, always vote for the mission that has the most chaos (hope your squad mates do also). After the 3 mini missions it will total up your chaos from the 3 missions and tell you what you have before the night defense. With some luck (each mini mission is random) and squad mates who are also hoping to achieve this, you will have 325 chaos or more.

If you are under the 325 chaos mark, it will not matter if you complete the night defense or not. This can be tricky and probably took me 7-10 tries until I finally got to the night defense with over 325 (we finished with 329). The best advice I have is be persistent and hope a little luck comes your way.

As for the night defense itself, it's pretty simple. You can place a machine gun turret type trap (rockets or anything that fires) on top of the the cat statue tray. It then has a good view of the "battlefield" and also won't be attacked by OD. From there the OD come down the alleyways so I suggest turret copters, acid sprinklers and any weapon with a good size explosion radius (TNT Teddy or Hairspray Bomb). With the alleyways being tight places, the OD funnel down them so your radius weapons have a good chance of getting a majority of them without using a lot of ammo. When you finish off the 3rd wave your achievement will pop. Good luck!

EDIT: Don't waste your time reading the solution just to downvote it. People are saying that most of the minigames mentioned here only appear nowadays in the Downtown map. I have no means to check that out since I've long completed the game and don't play it anymore. Anyways, I've came up with these ideas while playing it a lot and they worked for me. If they cannot be used for all maps any longer I hope that those who decide to read this solution will be inspired to seek and use their own creativity to find new ways to beat the challenges.

The first part of the job consists in getting the said percentage of Chaos from the sum of the minigames BEFORE the final battle (the Defend the Vats last stand doesn't add more Chaos to the count).

Here's the list of minigames I recommend picking and the ones I recommend avoiding when voting:

Wrecking balls - this is a good minigame to give everybody a chance to earn the bonus multipliers in the post game spin screen. Nobody is competing with nobody, except themselves. One bonus objective is to kill 20 enemies, the other to kill 40 of them.

Vending Vandalism - a nice game but one that requires excellent teamwork in order to complete it under 2 minutes. The first set of 9 machines spawn right where you are and everybody will probably take part in their destruction. As soon as the "Go to the next area" warning appears, instead of going towards it, if you're already used to this minigame and map, go to the third spot instead (it won't be marked on your screen so you need to know how to get there, which is easy, pretty much just follow the road hugging the invisible wall). Then, right after your teammates finish cleaning up the second one, the final 9 soda machines will appear and you can start destroying them, without awaiting for the rest of your squad. That's how you complete it efficiently in under 2 minutes.

Day of the OD - of all minigames, this is the one that I haven't played many times at all. So, no good tips here.

Fizzco Ambush - THE BEST mission in my opinion. Should be selected every time it appears in the voting screen. As soon as the game starts, pull out your Hair Spray Bomb (preferably equipped with the Second Amendment amp), jump forward and move down the road shooting everything until you don't see any red dots on your radar anymore. Keep bouncing on cars for extra points. Then start going back for that's where the next robot enemies will appear. Again, keep jumping on a car. When you get good on this mission, using the mentioned weapons, you'll get the most kills in it everytime. All in all, it's a short mission with lots of explosions and quick points.

Defend the Hospital - My tactic here is to stay away from your teammates from the beggining. As soon as the game starts, go South (check map) towards that big blueish building that looks like an underbridge. Stop between the numbers 4350 (on the right) and 4020 (on your back, on the left). From where you are, enemies will spawn in a few seconds, coming from 3 different doors. You can set up Acid Sprinklers and Turret Copters, besides shooting with your Hair Spray gun. Keep bouncing on the top of a car for extra points. It's guarantee that the biggest score and number of kills at the end of the round will be yours.

The Floor Is Lava - 1st golden hint: instead of rushing to the start point where everbody spawns, stay BY the Vat above the lava part (coming from the starting point of the mission, the first Vat to the right). That way when the mission starts, you'll be ahead of the others and really close to the first "pushie" doll. 2nd: after delivering the first doll, go back using the same upper way that you came from instead of jumping down and trying to slide through the lava like most people do. Keep doing that until you've collected as many as you can (I've collected all 6 a few times that way). Also, pay attention to your radar, it will show the locations of the dolls. Sometimes a couple of them spawn in a very safe area, away from the lava and close to the delivering point.

Scrambler... something - NEVER choose these "collect the numbers" kinda mission. They are one of the easiest to fail, no matter how hard or excellent one team member performs.

Fizzco HQ (a.k.a. "destroy the boxes") - In time I started hating this mission, for I was divided between finding and destroying 10 jedi robots for the bonus objective or focusing on destroying as many boxes as I could. Truth be told, it's hard to find more than 5 blue sword robots, left alone be able to kill them undisputed. Depending on the other option at the voting screen, I'd pass on this minigame.

Urban Jungle Gym IV - The least generous minigame to choose from. Only 1 player will get both bonuses for its objectives. After I grew a conscience, I stopped picking this game when I had a better option to vote.

If the tips mentioned on this solution help you in any way, please give it a thumbs up to let me know. Thanks!

I wanted to add this so other people don't run into the same issues as I did and can't understand what the problem is. This mission is by far the hardest to complete because the amount of chaos you earn is seemingly always between 300 and 320.

Having more people does not equal more chaos, I was successful finally with only 3 people. Killing enemies has no bearing on the chaos you earn. Chaos is strictly luck based for each of the 4 votes and the initial mission.

The only real solution for this is to keep trying and you must pass each mission. Best of luck to everyone!

Doing Chaos Squad with 2 people.

Nobody is playing this game now, and I am too lazy to go find a group. Me and a friend decided to tackle all Chaos Squad as two people and we have been successful. You have to set your Chaos Squad to private, invite the second person and then search. After a few moments it will put just you two into a game.

With only two people you have to be at the top of your game. You both will need all of your guns at level 5, and your other amps as maxed as you can make them.

The Guns we used were:
Hairspray Bomb w/ Second Amendment
Acid Sprinkler w/ Winter is Coming
Taunt Bot
Pulse Mine
Rager (Rager is better than Plague Bomb because Rage stops them from attacking the Vat. Plague does not.)
Swarming Nanobots
Freeze Bomb
Shield Buddy

You can use whatever amps you feel like, I never noticed too big of a difference except with freeze in the Acid Sprinkler. That is a must and will save your life.

For the personal Overdrives I would use OD Killer, OD Rival, OD Less Damage, Health upgrade, Deployable Ammo, and Single Shot Ammo. Damage on your guns is not terribly important because things are going to die anyway, you need sustained survivability and enough ammo to get through.

Always vote for the highest Chaos Squad in each mission. Generally if you vote that way you will reach the Chaos Squad goal. No matter what avoid Scavenger Scramble. The points one is unwinnable with two people. You really want the game to give you more Vat Capacity but you don't really have a lot of control over that.

The Night Defense has 5 waves. The first 4 waves have set waves of enemies. Once you defeat all the enemies the wave ends. The 5th wave is times. There is still a set number of enemies but it does not end until the timer is up. Even if you kill all the OD you can still lose if you get killed by Wingers. Speaking of Wingers, ignore them. Wingers, Herkers, and any other special OD. They will not attack the vat, so they do not matter. They will attack walls and traps, but the only thing that matters is killing the normal OD. This does make things difficult in later waves when there are a ton of Wingers around ruining your ability to grind, but you have to adapt and endure. With two people you can't focus on killing wingers and OD, and you gotta kill OD.

For each Night Defense I would put an Acid Sprinkler, Taunt Bot, and Pulse Mine in front of the gate. Then I would use Hairspray Bomb to attack. In the later waves when there is just too much going on I would focus on whats around the vat using Rage on large groups of OD. Acid Sprinklers around the Vat is a life saver.

For Traps I generally only used Senior Freeze. I would put them around the vat or in the path of the OD if the OD always followed a set path. Once there are a ton of Herkers and Wingers the traps get destroyed too fast. I would just put down a machine gun turret to help.


Little Tokyo Specific

All of the missions are doable with 2 people. The only one to really ignore is Scavanger Scramble as always.

Regenerating Herker is tough, but you are not timed so you can take as long as you want to win.

Attack of the Scabs is also a little tough just because it is easy to get overran and lose crates, but you only fail the mission if you lose all the crates so you can still win. Deployables are very useful.

Night Defense

You will have to defend 2 vats. There are a lot of directions the OD can come from but they all funnell into the middle area so it's really easy to kill whole groups.

The vats are very close together so it's easy to keep an eye on them both. There is also a good wire trail above the vats so it's easy to grind around and attack enemies.

No specific strategy is necessary. One person can focus on the outer area while the other focuses on the inner area near the vats. When it starts to get too crazy in the final waves both players will be focusing on the middle area. Hairspray Bomb, Rager and Deployables will keep things manageable.