Boss The Arbiter of ash

I'm having a lot of trouble with this boss and the only thing I'm confused about is how many times you can challenge the boss. Sometimes I get 5, sometimes 2, sometimes it's just one round and it's over. Also the boss has a magic circle skill and I have shoes that give me 15% movement speed so I can just barely run past it. But sometimes the boss will warp into my path and I die. I'm trying to figure out if you can make it not have body blocks and the additional challenge that's definitely there like an expedition boss.