This is the first boss. He is not hard to beat if you know how to deal with him.
When fighting the animals he calls in, just spam Y and they will go down quickly. If you can get them all on one side you can hit all of them with a single attack and not get hit in the back, but alternating Y attacks to the left and right also works.
The boss attacks with two patterns - one is a spinning attack where he stands in place, the other is a three-attack combo with him moving towards you. The easiest way to deal with him is to keep away while he is attacking and then move in for a three-hit Y combo. Don't get greedy! Do your three hits and get out. Since his three-attack combo moves him forward, you will eventually get pushed back near the boundaries of the room, when this happens just jump over him while he's recovering from an attack and move to the other side.
In the second half of the fight, the boss' animated staff will attack you. It moves up and down while homing on you. You can easily dodge this by rolling under it using LT. I found rolling worked better much than jumping. Do NOT get backed up against a wall by the staff or you will take a lot of hits.
When the boss loses all his health and stops fighting, hit him with RT to finish him. If you don't do this quickly, he will recover some health and keep fighting.
Don't forget that you can use your LB power for extra safety.
Like most boss battles, the key to this fight is patience. If you are like me and run in spamming Y hoping that the first boss will be a pushover then you will be sad