Every character has about half a dozen "Special Moves" and a unique Character Traits that are tailored to their fighting style. In order to view the Special Moves and Character Traits during the fight, you can pause the game and check their Move List. You can "tag" up to six moves with the , which will display them towards the top of your screen during the fight as a reference so you do not need to keep pausing the game. The best way to get this achievement is in Practice Mode because the timer and Health Bars are infinite. Be sure to read the description for every move, as some moves can only be performed while jumping in the air, while other moves can only be done when your opponent is crouching or jumping.
Go to practice mode and choose a character. Work your way through each character in order, to help keep track.
Once in game, go to PRACTICE OPTIONS and set METER GAIN to REFILL. This will give you unlimited meter for performing Supermoves. Next, go to MOVES LIST and scroll over to SPECIAL MOVES to view all the special moves for the character. Up to 6 moves can be tagged using so that they show up on screen for easy reference.
NOTE: Character Traits are required for this achievement and can easily be overlooked. Characters whose Trait is some sort of "Stance Change" - such as Hawkgirl, Nightwing, Raven, and Wonder Woman - open up additional Special Moves when they change stances. The Joker and Killer Frost can only perform their "parry" Trait if their opponent is attacking them. Lastly, Harley Quinn's Trait is only complete when you pull out ALL THREE items from her box.
Metahuman, Feel The Burn, and Superhuman Checklist & Video Guide