Gremlins

Ok so this is only a week late, but I'm a busy person people! Anyways, the other night I was sleeping peacefully sound and all of a sudden, BAM BAM BAM BAM! Right into my back was Jimmy's fists, 4 times! So I wake up the next morning and ask him what the heck he was doing, Jimmy:"The Gremlins had my arm, and so I broke loose and tried to get them back". Genny: "Gremlins?", "What?". Jimmy: "Gremlins".
So there ya go. Watch out for the Gremlins.

Which one is it?