Here's the trailer:
Eleven year old Brian finds a monster under his bed - Maurice the monster is actually really cool, and he leads Brian into his exciting world. You can reach the monster world by going under a kid's bed - very much in Monsters Inc. you go through a closet. The land under the beds is way scarier than Pixar's imagination though.
Monsters are susceptible to light, and if you shine a light on them, they turn into a pile of clothes - which is why they only come out at night. If a child goes down there for too long, they will turn into a monster too.
Some of the monsters are actually quite scary. Take this thug:
The most terrifying one is Boy, the leader. He's an overgrown man boy that always gets his way. The whole film feels quite dark for a kid's movie, and has more than a little Tim Burton in it. I really loved it, and wish I'd seen it when I was little.
Bonus video - Aaahh Real Monsters!
