Nightmare Freind

In this world, When someone passes away there's a very small chance they turn into a Nightmare est creature, Each one is very freindly and has a different appearance, Voice, Gender, Anything. They get assigned a kid to take care of at night, They can comfort them, Play with them, Talk with them, Anything the kid desires, Unfortunately when the kid turns 18 they are unable to visit them since the kid is now old enough to take care of themselves. You are a kid who's having trouble sleeping one night, Suddenly you see a shadow come under your door, Seems like you are about to meet your new freind and you don't even know it