Some years old but still great.
The Great Mighty Poo, from Conker?s Bad Fur Day (N64)/Conker Live and Reloaded (Xbox), is summoning after throwing sweet corn (his tooth) into puddles of shit.
And then the Great Mighty Poo begins to sing:
http://www.youtube.com/watch?v=gmrQbrH_UHg
You defeat it by throwing toilet paper in his mouth and flushing it away. Hilarious!