There's a little bit more posted in the above links, but let me summarize what the misery is/can do for you by copy/pasting:

It's a big ol' thing. It's a big ol' wheel, to be precise. The main body appears to be made of carved stone, which is partially covered by a writhing black mass covered in twitching red eyes. It has two more eyes that free-float around it and occasionally zip ahead of it. It has wings that are probably, like, several years overdue for a professional grooming.

It can float in the air and spin and shit. It can not float in the air and wheel about on the ground like any proper gravity-abiding citizen should, helplessly crushing buildings and slow-moving wildlife as it goes. It can also do other normal wheel things, like continuously cry a viscous red liquid from its two free-floating eyes that corrodes or burns through everything that it touches (is it blood? blood can dissolve rock, right?).

On top of this is the power-null of a mile radius, though I don't think Kili himself will run into much of an issue in regards to this. It is entirely possible to have Kili be killed by the Misery during the course of it's party-crashing horror.