Have you ever been very frightened and had your mouth go completely dry? You have no saliva, you have no "spit" - you are "spitless."
Actually, there's another word that's more commonly used here, but it's a rude word, so the comic book was trying to keep it clean.
"Got me" means I have no idea, I have no information on that, I can't tell you because I don't know myself, etc.
"He had it coming" means he deserved what he got. The "now" was just an introductory word with no real meaning.