The secret to most of these "perform this move" achievements is to go right to the challenge section and take the tutorial. The tutorial will force you to perform a lot of these actions, and the achievement will count as you do them.
This is won when you perform a launcher super attack (always the one on your left) followed by another super attack to chain together a 2 hit combo. As you play with the different characters, you'll find a few that you like. Personally, I find Magneto's motions very fluid, and can easily perform continuous 3 hit combos with him.