Bonechill is one of the last main bosses in Super Paper Mario. He can attack by using his icy breath that can also form icicles on the ceiling, or by firing ice bullets from the cannon he sits upon. He has a max HP of 80 and has an attack of 4 damage. He was stuck in a prison in the Underwhere along with his Skellobit army. Count Bleck set him free to destroy Mario, and steal Luvbi (who is actually a Pure Heart). He fails (of course) and shatters into bits. It is told that he was once a Nimbi, and it is also indicated by his multiple wings on his back. He is fairly easy to beat if you use Luigi with Dottie (since when small, his attacks are quite easily avoided), and use Luigi's Super Jump on his head from below.
He appears to be very clever and cunning due to the fact that he determined that Luvbi was a Pure Heart without much information given, although Count Bleck may have known and told him something along those lines.