Final Valhalla boss

Was cruising through Valhalla fairly easily. Got to level 3 tyr when he says he has one last weapon to show me and what the fuck he ate my ass so quick I wasn’t even barely doing damage to him and I couldn’t avoid anything.

The jump up in difficulty is insane. Instantly considered un installing after I woke up on the shore.

How the hell do you beat him? I need advice,