Here is the full list of all 36 88 Heroes achievements.
Destroy 88 blocks in a single game
Kill your first enemy
Kill 8 enemies in one game
Kill 88 enemies in one game
Kill 888 enemies in total
Score 8,888 points
Score 88,888 points
Score 888,888 points
8 Perfect rounds
16 Perfect rounds
32 Perfect rounds
Complete the Office
Complete the Sewers
Complete the Volcano
Complete the Space Station
Complete 88 Mode with 8 heroes remaining
Complete 88 Mode with 16 heroes remaining
Complete Magnificent 8 mode
Complete Solo mode
Complete any room in under 3 seconds
Complete a level with zero seconds left on the clock
Complete your first room
Revive a hero
Play the game 88 times
Finish with 8 minutes (or more) remaining on the Doomsday Timer
Collect 8 small coins
Collect 88 small coins
Collect 8 large coins
Collect 88 large coins
Die for the first time
Die 8 times
Die 88 times
Die 888 times
Kill every unique hero once
Kill any hero 8 times
Kill any hero 88 times