Killer Instinct

Easiest character I've found to get this with is Riptor.
When a tank chest appears, run or jump to it quickly, then simply hammer the heavy punch button. The fire breath move will fill the meter with about three seconds to spare.

You will sometimes get a Tank chest at the end of the match. It is the one that has a meter to fill. You will have to do combos on the chest to fill it up. Once you get to x2 (200%) you will earn this achievement.

What I would do especially if you are having trouble with this is to get a consumable that gets you unlimited shadow meter and have at it.

You will occasionally get a Tank Chest at the end of a match (many times the story option you choose will show you that a Tank Chest will be available if you win a battle).

I personally used Riptor. I opened with a medium kick combo and just before it ends I use both my shadow moves and a heavy finisher (make sure you have a full shadow bar at the end of the match, easier if you do an ultra).

If the bar hits 2x then you will unlock the achievement (this is classified as doing 200% damage).