Batman: Arkham Origins

This set of 15 challenges are as follows

-Perform 5 Counters
-Use the Quickfire batarang 3 times while in combat
-Reach x8 Combo Multiplier
-Perform 3 Special Combo (Y+B) Takedowns
-Complete a fight without leaving focus mode
-Score a combat variation bonus of 3 or more in one fight
-Knockdown at least 3 enemies with explosive gel
-Knock down 2 enemies in one slide
-Perform a counter in the middle of a beatdown
-Get an A grade in a fight with at least a high threat level
-Use the power gadget ability 3 times
-Perform 20 critical strikes in one free flow combo
-Reach x30 multiplier and perform 7 variations in a single fight
-Take out 3 or more enemies with one use of the multi-ground takedown
-Complete a fight with a medium or higher threat level without being hit, with a x50 combo and at least 15 variations

I would recommend starting theses as soon as possible on your first play through. Some of the challenges cannot be completed until you acquire a upgrade, some of which are unlocked through most wanted side missions (critical strikes is unlocked by completing Shiva), if you cannot yet complete a challenge, figure out what you need and try to get it done sooner rather than later because the longer you wait to do some of these the more difficult it may get (enemies have more variation later in the game).

Crimes in progress are an excellent way to find decent sized groups of enemies to fight.

As a side note, some of these challenges I believe to be heavily bugged, for instance I unlocked the final challenge (50 combo and 15 variation) on two enemies when I glide kicked the first one and did standard strikes on the second and reached a x5 combo. A similar thing happened on a similar challenge requiring 7 variations when I used the shock gloves).

Some solutions should be obvious core gameplay (counters, quickfire gadgets), you will have to be a master at this game's combat to get this achievement so I will go over some of the trickier ones briefly.

For the slide I just ran around in circles and made a train, turning around when they were nicely lined up and sliding right into the train.

Freeflow is achieved after an upgrade and reaching a combo of x12. Using a quickfire gadget while in this mode has to be done 3 times for a challenge.

20 Critical strikes it about timing, I would recommend not using shock gloves and just getting a x5 combo then only using strikes and counters on a group of about 6 or 7 enemies, if you time your button presses well you can strike between the group of enemies regardless of range and score critical strikes which increase your combo by 2 with each hit. Critical Strikes are not unlocked until after beating the Shiva Most Wanted Side Mission.

For 3 enemies in one multi-ground takedown, just strike several enemies quickly (having freeflow focus active may help) and once you see 4 (one will most likely be up before you can get him) on the ground, press A+B.

For the variation challenge you will need to use the majority of the move in Batman's arsenal for the 15 variation:
-Strike
-Counter
-Evade
-Cape Stun
-Ultra Stun-
-Ground Pound
-Beatdown
-Aerial Attack
-Y+B Takedown
-A+X Bat Swarm
-A+B Multi-ground Takedown
-X+Y Search and Destroy
-LT+X Explosive Gel
-LT+Y Bat Claw
-LT+B Concussion Detonator
-LT+LT Batarang
-RT+RT Glue Grenade

That is 17 (there are more possibilities), so pick the two you hate the most and leave them out, or start with a glide kick which may count as an additional one. Shock gloves with these moves count as a different variation. Other things like the blade dodge takedown and shockgloves used in conjunction with gadgets also may count as a separate variation.

SPOILER: THIS PARAGRAPH ONLY At nearly the end of the game there is a section in Blackgate prison again, there are some good groups of enemies in there for doing this achievement, but some of them contain enforcers and martial artists, both of which I suck against. You can probably knock out some of the combo challenges on these groups. I would recommend using the shock gloves to focus down the enforcers immediately so that the only things left are basic enemies.

Good Luck

OK there seems to be confusion on Challenge 15: Complete a fight with a medium or higher threat level without being hit, with a x50 combo and at least 15 variations

While I do believe its bugged, as the way it reads I think it is suppose to be done all in one fight, you do not have to at this moment (may be patched in future update)

As of writing this I have gotten this challenge 3 times on 3 different save files as well as a friend getting it twice more the same way.

For this challenge all you need to do is complete the 3 different objectives at some point once the challenge has been unlocked. They DO NOT HAVE to be in the same fight. As long as you complete a 50 combo, perform at least 15 variations, and complete a fight without being hit over the course of one play-through this should unlock.

This also works for all other multi part challenges. I did the stealth one in 2 different fights. I did 5 different takedowns in a low threat level stealth area, then completed an extreme level open fight and the challenge was completed after the open brawl.

Note: I have had reports from friends that it needs to be done in one sitting and without dying in order for the game to recognize that the challenge has been completed.

Note 2: I did not see it listed but for those that are just starting the game the challenges must be completed in order and the next level of challenge will have no progress added to it until the previous challenge has been completed.

ok i hope this helps but for the 50x combo i went to the diamond district were the spelling of it is on the map. on the road down there is a bunch of guys one of them is armored. altho you can get it fighting others, its just a big area with bad guys, a couple guns didnt bother me if i had to fight the other ones. BUT once your done and you get a 50x multiplier you CAN drop it without the 50 being there. then fight other fights and do 15 variations. hell i did 3 fights and the achievement unlock because on my second fight i got so many in. but on the 3rd i did more that i missed from the second fight and boom, achievement unlocked. have fun.

Just a quick suggestion for level 15. I achieved this during my New Game Plus play through.

This might be a spoiler, as I will describe the room that I was in.

Anyway during the story, and on the bridge when you're disarming Firefly's bombs, right before you get to the 3rd bomb is a room with about 10 or so enemies of different types. I used the Disrupter to neutralize the one enemy with the gun and the 3 of 4 gun boxes in the room. After that, I lead with a smoke pellet into the middle of the room. Everyone starts coughing and hacking except for the one guy with a shield, so I ran into the middle of the room to take him out first. Then, I bounced immediately to one of the armed enforcers, cape stun and beatdown on him. This got my combo up to around 15 or so. At this point, everyone is still coughing and hacking and decently spread out. From there, since my combo was high enough, I could ping pong around the room attacking one enemy and moving on immediately. I started throwing in various moves and combos in order to get my variation bonus up. Note that this room has electrified walls, which need to be avoided. I'm not sure if damage from the walls would cause you to fail this challenge or not. But I didn't want to take the risk and restarted if I took any damage of any kind.

The best part, if you get hit, just restart. You'll go right back to the entrance of the room and can replay the fight as many times as needed. The only problem is, while you can easily tell whether you've been hit or not, you'll have no guarantee of whether your variation is high enough until the fight is completed. But, I've found it is not that hard to get up to a 14+ variation. Just use all the tricks you can think of.

Obviously, this doesn't need to be completed in that room specifically. There are many groupings of enemies throughout the story. So, that is my main suggestion. Do this during the story when you find a room with a good amount of enemies. That way if you get hit, you can restart as many times as you need. If you try to do this in Free Roam, you'll be spending a lot of time searching for areas with enough enemies to get the fight completed with a high enough combo.

Just my two cents.