"The Kaull's level three alt-fire (charged) or a level five Aeon Beam (charged Aeon Pulse) will do all three required hits to defeat the Skinwalker--the giant ape boss--in chapter six Turning Tides, speeding up the battle significantly. Unfortunately, this boss' pattern is largely random, so there's not much you can do besides wait until he decides to drop a rock from the ceiling.

You can also use Lift on the rock he throws to shove it back in his face, but this is the worst way to try to fight him in the PC version, as the scroll wheel isn't very accurate and often targets the debris around the arena first. On Xbox, it's quite easy to flick-target the rock and beat him that way.

Instead, assign Surge and then hold the mouse button to charge it, and unleash it while the Skinwalker is holding the rock above his head. Then you can wail on him with whatever weapons you want. You'll have to do this three times if you don't have the Kaull's Energy Blast or a level five Aeon Pulse.

For reference, the Skinwalker has 4000 health, and after you've dealt 1350 damage to him, he recoils and begins his attack phase again. You can deal more than 1350 to him in a round if your last hit is powerful, though, meaning it's quite easy to beat him in two rounds as well."