The Space Slime is a one-shot minor antagonist of the reboot TV series, Ben 10. He first appeared in the episode, That's The Stuff.
That's The Stuff
The Space Slime escaped from the container, then it saw a rat, then it shapeshift into a rat. When Ben transformed into Grey Matter, he saw the rat, then it shapeshift into Grey Matter. It later met Gwen and Grandpa Max and it shapeshift into them. Ben transformed into Omni-Enhanced Four Arms. That slime also shapeshift into Omni-Enhanced Four Arms, but it can't do omni enhanced powers. Ben realized that the slime's weakness is its own reflection. Ben transformed into Diamondhead and made lots of mirrors and defeated it.
The Space Slime appeared as an ordinary purple slime, but it is a living creature that can shapeshift into almost anything.
The Space Slime is a destructive mindless monster that only cares about destroying.