HOW TO CLEAR LEAFA'S REQUEST AND BEAT GLIMODOOM ON EXTREME MODE

This strategy is pretty easy to be honest, I went for a sniper Rifle but you can do this with every weapon in the game, just keep running around and hit the palm of his hands while charging or while he's attacking you, you'll be able to stun him that way, just keep the process until he's dead.

For a detailed walkthrough check the video below: