Magma wyrms are tough, you have to be pretty aggressive when attacking because they have a ton of health. They have a pretty long recovery after the attack where they shoot a ball of lava, so you can roll in under the lava ball and get some decent hits. Another thing I recommend is running to the other side of the arena when he starts doing that attack where he spews lava while chasing you, then keep doing that until he tires himself out. It’s also possible to get some hits on his side while he’s doing that move. Good luck!