This is more of a technique than a cheat. It helps you to kill elites. Heres how you do it: First, you need a plasma pistol and a human pistol. When you have those, use the plasma pistol first. Charge it up completely. Once charged, shoot the elite anywhere with the fully charged plasma bolt (taking off his shield). After that quickly take out your human pistol and shoot the elite in the head. Note, this will kill any elite instantly if done right. If you don't shoot his head, it only takes a few body shots.