Originally Posted by BigNev44
And keep in mind that you have to KILL your enemy or enemies after building up the combo at 300 (while the combo is active)
3 buddies including myself thought the achievement would pop after the combo was built to 300 but it pops after the kill.
You do NOT have to kill them. Just let the combo go out after 300 on its own (I.E. not by getting hit) and it should pop. I got 301 on the first set of enemies in the second to last level and just jump/teleported away until it ended on its own and it popped. The enemy I hit 301 on was still alive.