Batman: Arkham Knight

First thing's first, on this combat map, enemies will continuously spawn into the arena as you continue to take out thugs. Thus, there are no "individual" rounds. At the start, it's just a few unarmed hostiles, then it gets increasingly difficult over time, in this order:

• Stun Baton, shield bearing thugs, and Medics who revive and "electrify" their buddies, will begin to spawn in after a while
• Eventually, Ninjas will join the fight
• Later on, thugs will begin opening the weapon crates to use guns
• Finally, Brutes will join the mayhem

Now in order to face off against Killer Croc, you will need to obtain 20 Gotham's Greatest points...or in other terms, achieve a score of 1,050,000. Once you've reached this score, enemies will stop spawning into the arena, which means you'll have to wipe out anyone who's left at that time. Once the ring is cleared, Croc will jump in (as will Nightwing) and a Dual Play encounter will ensue similar to Killer Croc's boss fight in his Season of Infamy DLC mission. 

Take note that while you will regain any lost health once Croc joins the fray, your armor will not replenish. On top of this, Batman and Nightwing share the same vitals. Remember to dodge the villain's attacks while beating up the thugs that join the fight as a means of building up the Dual Play Takedown meter. After 4 Dual Takedowns, the next 2 will be a quick-time event in which you counter Croc's swings and perform Beat Downs (X repeatedly). Once Croc is defeated, the achievement will unlock and the fight will carry on. 

This achievement requires a tremendous amount of skill. In what seems to be an impossible feat, the only plausible way to obtain the 1,050,000 point requirement is to obtain a 450+ hit combo. That means as soon as the round starts, you can never allow your combo to break either by self error (accidentally countering when no one is attacking) or by getting hit. Even if you lose your combo at 290x, and think it's okay to carry on and amass another 290+ hit combo, it simply won't work that way. 

There's no other way around it: You must achieve a 450+ hit combo and never have it fall.

Now there are over a dozen combat tips worth sharing for this achievement. A massive thanks to Batman Arkham Videos, Duke of Darkness, ScorchPSO, WACKY WOOKIEE, and AgentGinger419 for all the insight. 

Basic Combat Tips

• Evading/Leapfrogging (A+A)
  • Abuse it. This move will be your best friend. You will jump over the heads of your enemies, giving you time to survey the arena and pan the camera around to where you need it to be. When you land, act quickly and make your next move so your combo doesn't break.

• Countering (Y)
  • Don't neglect the basics of countering an enemy attack when the blue "counter" icon appears over their head. Don't try to strike back or you'll just get hit and lose your combo. Counter their attack, or in the worst case scenario, leapfrog away.

• Striking (X)
  • Know who to strike and who not to strike. Medics and standard thugs (unarmed or gun wielding) can be hit without worry. Shield bearing thugs cannot be hit, and neither can Stun Baton wielding thugs (from the front). If you want to strike a Stun Baton thug, leap over their head, then strike them in the back. Ninjas will leap away the minute you try striking them from the front, so like Stun Baton thugs, get them from the back. Lastly, avoid striking Brutes entirely.

General Advice/Guidelines

• At a 100x combo, you want to try to have your score at around 50k.
• At a 200x combo, you want to have your score sit between 180k and 200k.
• After you get a 300x combo, stop worrying about your score; stay focused and don't let that combo drop.
• Once you have a 200+ combo, stop using Batman's Disarm completely and start using his Combat Takedown (B+Y) every single time it's available as it nets 10k+ points.
• At a 250+ combo, use the four generators on the outside of the ring to get Environmental Takedowns (A+X near the generator when an enemy is highlighted in blue).
• When Brutes spawn into the ring, throw a quickfire Freeze Bomb (RT,RT) as it automatically locks on and freezes one Brute in place for a little while.
• You want to try and have your score at 850k+ before the Brutes start spawning into the fight, otherwise it gets to difficult and hectic.
• If you can manage it, pick up dropped baseball bats (A+X) when your meter allows for it; baseball bat strikes can penetrate anything including shields, Brutes, Shock Batons, and electrified enemies. Spam it until it breaks.
• The moment your combo breaks, restart the challenge right away. Never carry on. The only instance you may want to attempt to carry on is if it breaks at around a score of 950k or higher.

Gadget + Enemy Variant Tips

• Standard Thugs
  • At the outset, you have nothing to worry about with the standard thugs. The key here is to get critical hits by striking the enemies with perfect pacing.
  • Critical hits add 3x to your combo, rather than 1x.
  • You will want to try and hit a 100x combo at around 50,000 points before the majority of the Medics, Shield, and Stun Baton enemies spawn in.

• Medics
  • When the Medics join the fight, they will begin to revive fallen hostiles and "electrify" other thugs.
  • You must perform a Batclaw Slam (LT + Y, then X) to disable their electricity field.
  • The Batclaw attack will automatically gravitate to any electrified enemies and you are completely invincible to attacks during the animation
  • Get rid of these electrified enemies as soon as you see them, and don't worry about Medics reviving fallen hostiles (seriously, don't worry about that).

• Shields and Stun Batons
  • Enemies who wield Stun Batons cannot be struck from the front; you will need to leapfrog over them to hit them in the back.
  • You should prioritize using Batman's Disarm attack (X+Y) to break their batons.
  • Alternatively, you can use the quickfire REC (LT+B) to knock them to the ground as it will make them drop their batons.
  • Shielded thugs are a hassle, and cannot be struck from the front or the back.
  • Avoid contact with them all together unless you are performing a Disarm attack as a means of breaking their shields.
  • Alternatively, you can perform an Aerial attack (B+A+A) to strike them; you are completely safe during the animation when doing this to shielded thugs, but you are vulnerable to hits when doing this on standard thugs.

• Ninjas and Gunmen
  • If you're comfortable performing Blade Dodge Takedowns against ninjas, then by all means, do so as they net a lot of points.
  • If you're rusty or feel as though it will mess you up, avoid a ninja's strikes entirely by leapfrogging over or away from them.
  • Gunmen aren't too bad and the camera will automatically snap to them as they are reloading and getting ready to fire their weapon.
  • When the camera snaps, your next strike will always gravitate towards them.
  • If you quickfire a Batarang (LT+LT) at this "camera snapping" moment, it will always gravitate towards them and knock them down.

• Brutes
  • Brutes will spawn into the fight very late and hopefully you have the needed score before ever seeing too many, or any at all.
  • Their attack speed is insane and their attack range/reach is dangerously long.
  • You need to avoid contact with them all together by leapfrogging over their heads and avoiding strikes of any kind to them.
  • Only engage a Brute when you can perform a Combat Takedown (B+Y).
  • Street Brutes (wearing jeans and a jacket) take one Combat Takedown to eliminate, while Militia Brutes (wearing military gear) take two.

And that's it. Hopefully the supplied strategies and tips shown above help you on your journey with this achievement. It's tough and insanely skilled-based, but the most persistent and dedicated players can it have it done in time. For reference, it took ScorchPSO only 1 hour to get it done, while I spent about 7 hours worth of attempts before unlocking the achievement. Persistence. Remain calm. Don't lose focus. 

For some motivation, and a look at how the most skilled Arkham player obtained their 1,050,000 in just seven minutes, feel free to check out the video below. You might even learn a few new tricks. Thanks, BAV, for everything.