Thanks. I updated my original post with some more info too. Since using Ray of Frost my Hydra was doing basically all of my damage because I could never stop moving. I'm good at avoiding the cages and never get caught, the problem is the spirit phase where he blinks right up on me while Diamond Armor is on cooldown. I just can't get away from him. Without Force Armor it's easy to get two-shotted so I'll probably keep that...
I haven't tried Arcane Orb yet though, I'll give that a go.
EDIT: This is a stupid question, but how do you cast spells without stopping? I wasn't aware that was even possible. When I cast Arcane Orb my character still stops...