There are several good ways to take out the cheiftains:
- Plasma weapon for shields, then a single-shot weapons for the helmet/head
-Use a Gravity Hammer, but make sure you actually hit him. If you miss, he'll hit you the moment you're next to him.
-Grenades. Lots of grenades. Stickies bounce off of their armor, but frags and incendiaries work quite well.
-If they do a short hop towards you and swing, try to jump over them. If your sensitivity is high enough, you can turn around in mid-air and assassinate them.
-If there's more than one person playing, make him charge towards P1. P1 then jumps out of the way while P2 bashes his head in from behind.
-If you do try to use Heavy Weapons (Rockets/Fuel Rod), make sure that you hit him more than once and that you hit him quickly. If you land one hit, but then have to reload, the chieftain will turn on his invincibility.