Nyan Cat is a meme which is able to be spawned in Scribblenauts Unlimited. It comes from a famous youtube video in which a cat which appears to have a poptart as a body flying though space with a rainbow trail, accompanied by music that says "nyan" repeatedly.
Nyan cat can be seen in the E3 preview of Scribblenauts Unlimited.
People will eat nyan cat, probably because his body is a poptart.
If you put a Nyan Cat into a toaster, it will light up as if a bomb was triggered, fly upwards shortly after and explode into three rainbows.
This is a reference to a YouTube video showing Nyan Cat being born by flying out of a toaster.
If you give him the adjective ridable you can use him as a mount.