Iron Man 2

This achievement should come naturally with normal gameplay as Iron Man, especially since his lasers (once fully upgraded) are his best weapons. However if you have not obtained this achievement by the end you can get ~30 kills in about five minutes by grinding level 4. Once the level starts hit the buttons and enable the trip lasers, then as you descend trigger all three, and each trigger should release about ten robots. Dual equip lasers and kill them all. After that go through the tunnel and destroy the miniguns to get to the checkpoint. Save, quit, and repeat as needed.