If there are any of you struggling with this challenge, there is an easy way which I found out when doing the challenge in the 1st round of the "Flawless" map.

Start by just attacking them with the gadgets. You don't have to be in freeflow. So do sticky bomb, electric, freeze, batarang and batclaw. That's 5 variations there.

You can then start your freeflow. If you are doing it in the "Flawless" map or any map that has an environment, I suggest to start the freeflow by doing an environmental takedown. Then do an aerial attack and redirect aerial. Then do the 3 special moves: Combat takedown, weapon disarm and multi ground takedown. That's another 5 or 6 variations depending on if you do the environmental takedown.

Then finish of the fight with a knife dodge takedown, beatdown, aerial juggle and ground takedown. That's another 4 variations.

The last variation is counter which you will get during the freeflow anyway.