This achievement is won by gold starring or getting a three batarang rating on all of the freeflow challenges. There is no specific way to get this achievement therefore I'm going to give tips and advice. A bit of warning, this achievement is a controller smashing, screen breaking, anger inducing achievement that should only be attempted by the brave and the bold. This achievement is pretty much 50% skill and 50% luck so it's not gonna be a walk in the park. Another warning, to make getting this achievement easier have the upgrade that gives you critical hits 2X, the combo takedown, the throw upgrade, and the upgrade that lets you use combo takedowns at a 5X multiplier instead of 8X.
Intensive Treatment Challenge: 18,000
This one is the easiest of all the challenges seeing as it has very few enemies compared to the others. The enemies here are all standard thugs who will occasionally grab pipes to bash you with. Counter, combo takedown and ground takedown them to get a nice multiplier.
Sewer Bat: 18,000
This challenge is a bit more difficult than the previous because you have more enemies to deal with. Starting in second round you have to deal with thugs with knives. Probably the most key thing to remember when facing them is to never attack them when trying to rack up a combo because they'll stop it dead in it's tracks. Try to combo takedown them as soon as possible so that they're out of the way. If you can't do that then stun them first and start your combo (Note: Jumping over them and trying to attack them from behind is pointless because they'll instantly block it, destroying your combo in the process). Knocking out the knife thug should be your first priority in later stages seeing as they can pretty much destroy your combo. In the fourth round you encounter thugs who pick up cinderblocks (or something) and throw them at you. Just hit them or grab them before they can throw it at you so you won't lose your combo
Shock and Awe: 30,000
In this challenge you have to race against time to beat all the thugs in each round (Note: You have to beat them within the time limit or you automatically die within a few seconds). To make matters worse in the second round you'll face off against a thug a with stun rod. The strategy for these thugs is the same as with the ones with knives. The only difference is that you can jump behind the stun rod thugs and hit them to continue your combo. In the third round you face two knife thugs so rack up a combo and use your combo takedown to dispose of them. In the fourth round you have a big group of enemies with a knife thug and stun rod thug as well. Use the other to make a combo and take out the knife thug, then go after the stun rod one.
Rumble in the Jungle: 30,000
This challenge has you facing off against a lot of enemies including knife thugs and stun rod thugs. This is also the first time you encounter a thug who a gun off the wall. If you ever see a thug with a gun, take them out as soon as possible. Not only will they destroy your combo from afar but they can also deal a lot of damage Batman if left unchecked (Note: Even if you take out the gun thug, be wary of other thugs picking up the gun and using it). Once you get to the fourth round you'll fight a bunch of thugs and one titan. When it begins charging at you throw your batarang at it's head and dodge him. Begin attacking him and counter any thugs who try to attack you. Once you weaken him enough you can ride him and whack the thugs, increasing your multiplier. To this until the beast and all the thugs are out of the picture.
Intensive Treatment (Extreme): 30,000
The same as the normal version, just more thugs, and the occasional cinderblock thug.
Sewer Bat (Extreme): 50,000
This again is much like it's normal version but with a lot more thugs. You have to really be careful here because there are a lot of thugs who will pick up cinderblocks and guns to try and wreck your combo. You'll also have to face knife and stun rod thugs, use the strategies I mentioned before to bring them to their knees... or break them.
Shock and Awe (Extreme): 30,000
This challenge by far I think is the hardest of them all. In this challenge you have to face off against more stun rod and knife thugs then ever before. On top off that you still have the timer and getting your flow messed up makes it harder to win within the time limit. My biggest advice is combo take down every knife thug you see to make your life easy because if you don't, they'll make it a living hell.
Rumble in the Jungle (Extreme): 50,000
This challenge to me seems easier then most people believe. By now you know what to expect, lots of thugs, knife and stun rod thugs, cinderblocks in the air, bullets flying. But what makes this challenge special is the fourth round where you face off against two titans and a sizable group of thugs. The most important thing here is to use the titans against each other. Once one of them is stun and primed for riding, attack the thugs first and then the other titan. The main reason being that you get a bigger combo and that after hitting the other titan three times, you get throw off. If you did it right the other titan should now be on the ground in the stun stated and you should be able to continue your combo and repeat the process. By doing that I was able to get to the number 2 spot on the leaderboards... no bragging intend just wanted to show it's an effective strategy. (Note: If a thug gets a gun while you're riding a titan, take them out as soon as possible because they are the only enemies that can stop your combo as you ride.)