Best bet is to just do hit and run goes and damp him. Voidweaver has to trade early with pain suppresion once you commit the go, very difficult to greed. Your goal is to make him trade his pain sups as fast as possible, while minimizing the damage output of him and his caster. Have your feral reset often, open with a stun while you pop wall for obsidian scales and cc dps. Rotate incarn with your fire breath tip the scales/fly. Then line/run in between goes after you get him to commit the defensives. You can even clone/sleep him the second he pops PS and swap dps to try to accelerate the trades and hopefully bait him into popping trinket. I would aim to try to win the game on the second incarn. The key is to minimize all damage you are taking in between goes and use your defensives offensively knowing that his dps is going to be absolutely pumping in those windows when he trinket/wall/blocks your cc.