I am learning to play dungeon world I'm wondering in a druid shapeshift the animal has moves, right like a bear can maul. if a bear mauls a creature is that creature done for? Or does the druid roll damage?

Depends on the needs of your table, which if you're not the GM, you'd obviously want to air out their concerns. It's been a while since I looked at DW, so I'm a little rusty, but is there an actual Bear stat block? Because if their ability to maul itself has a damage stat, then you'd also have a damage stat (but it would be your own). I as GM would personally consider other avenues too, like if the bear has a claw that has a damage roll, but the maul doesn't I'd maybe let the maul be the better of 2 or 3 rolls on the logic that it's a claw, claw, and bite.