The first time I found him in the elven lands, I tried beating him without the turtle's help. He had 50 INT and was really fond of spamming chain lightning, but he can't cast it if my dryads won't let him
I got "that's how the shaman ended his days" again. I wondered if the turtle does anything else for you later on, if you don't request his help here.
(Later I went back and beat him the normal way, since the turtle gives you ~15 crystals in the process.)