Gah! How could I forget my favorite enemy could shoot? Well technically it's the dormouse that shoots at you... but no matter or something.
Building on what Risp said with the mechanical body parts, it'd be cool to see that in a boss. Like a cross between the Mech Turtle from JJA and the Schwazengaurd...
First it'd use it's tried and true Something-rang(can't think of the name) and if that misses, he'll try to attack you with a super arm until the 'rang came back. Once he's low on health he'll throw more than one 'rang at different times. If all else fails, he uses a cannon in his stomach and mimics your ammo to attack you. Only the ammo would be a pwered up version.
Edit- And it seems the BBB has made a nice transition into 3d, I wonder how it plays