Roomy is the unholy spawn of the house and Silent Hill.
It's the DMs' greasy cousin.
The house is an evil entity that can travel large distance by teleportation, and it just so happened to teleport smack dab in the middle of Silent Hill. Angry at the intrusion, it tried its best to destroy it, but find for reasons unknown it couldn't even scratch the house -- that is until it was able to lop off an entire room.
Seperated from the main body, Silent Hill created something born out of its reality-bending powers and the house's own materials that could find and boot it out of its perimeter for good.
Said something immediately disappeared, never to be seen by Silent Hill or the house again.
I mean, there's really not much to it, is there? From the moment of its conception it decided to go against its purpose and do whatever the living fuck it wanted to, feeling an immense inclination toward evil. It gets around, you know? it's sadistic, a little perverted, chaotic, messy, outspoken, and absolutely shameless. In the words of Griffin McElroy, a fun-havin' fun-lovin' dirty boy. Or.. room, as it were. It loves taunting people and keeping them inside itself as long as it can before killing them, just to bask in their reactions. Somethin' feels so damn right about being feared and hated.
It.. doesn't really know why it does this, it just sort of does. I mean, does a bird questions why it can fly? No, dumbass. If Roomy pauses long enough to consider itself it's pretty sure something bad'll happen. Roomy's not sure what, but it'll happen, and it won't be pretty for anyone.
It. It's just got this itch that can't be scratched unless Roomy.... well, ya know. And it feels sooooo goood to scratch.
Despite how much it seems to delight in hurting people physically, it holds no interest in being any other kind of evil.
Roomy is a living entity that can 'possess' (almost) any interior space that's big enough for a person to walk into and fully shut the door. Once possessed, the area inside can change into any shape or structure Roomy pleases, the dimensions of which don't matter -- for example, it has crafted a cafe inside a broom closet.
Usually, Roomy uses these abilities to lure people inside where it subsequently kills them, usually brutally.
It is also capable of projecting a sort of genius loci, a humanoid (usually with one or two limbs missing replaced with metal blades, bloodstained with diseased skin, a welder's mask and long, greasy black hair. It can move outside of the Room, but the farther it goes the more it starts to fall apart.
[relationships with family, other characters, etc.]