Not that it makles any difference, but his name is Doopliss. Go to Twilight Town and find the Superbombomb to make Vivian join your team. Next, head back to Creepy Steeple (dodging 'Mario' on the way) and drop down the well. Try and avoid the Buzzy Beetles. Push the barrier up the slope and press X. It will go straight over your head. Drop down the hole at the end and go left into the room which was locked earlier. Open all of the chests, stand next to the parrot, and press X. After learning your nemesis's real name, find him and use this name. He'll run off to Creepy Steeple. Go back and kick his face in. Simple, really.
10000 posts at last! w00t! Okay, I'm off into a quiet retirement. Don't bother me.