|This is actually a very easy achievement since you can't die in multiplayer. However, if you wish to try to reduce your damage, the best way to avoid taking damage is to stick to the sides and avoid staying in the middle whenever possible. Keep an eye out for shield recharge drops which sometimes drop from random enemies.|
The boss will have one stack of smoke billowing out of him when he's at 75% health, two stacks of smoke when he's at 50%, and three at 25%. As soon as either one of you defeat him the level will be complete and you'll both get the achievement.