Tips For The End

Finally close to the end. I'm on the brain, trying to get to the crown or karsus. What's the best strategy for getting over there? I've seen invisable potions and globe of invulnerablity, then claim it with the mindflayer. In this case, Orpheus, but I don't have those potions.

I know there's one mission after this. I have most summons left, but don't know what I'll need.