I'd have to say the coolest bosses are... Sigma from Megaman X4, Bass fused with Treble in Megaman8, usually all the Zelda bosses, Kain, Anubis from ZOE2, that guy from Marvel VS Capcom2[I can't read his name :(], and ALL the Bretherin from the Legacy of Kain series. The Bretherin kicks arse