For this achievement, you need 4 players to trigger their special abilities at once. I used the level HuangHua Temple as it has weak enemies infinitely spawning at the very beginning. I stayed at a safe distance to not get killed and just one by one, combo'd till my meter was full.
You don't need to press all the triggers at the same time, so long as you activate the abilities while others are active. I pressed the 2 triggers on each controller one by one and it worked.