Sluggish Pet Rat with Diarrhea, Porphyrin, Cold to the touch -- WON'T EAT?!?

He sounds very sick. Clean the diarrhoea off his but (warm water is fine) and them get him to the vet as soon as possible. He will be dehydrated so the vet may give him fluids and medicine. It souldn't cost two much; just consultation and for the tiny amount of medicin he may need. Be prepared for the worst though; he doesn't sound to good. If the you do get him home agin then leave him in his carry case untill you have given his cage a good clean to remove the poo. Make sure his water bottle is within very easy access to his bed.