The only seen group of outsiders so far were Nofun mutants armed with Crushestro weapons that attacked Riff and a few members of the Resistance at the beginning of 4U City Green. However, alt-Torg commented that these mutants were only one kind of Outsider, and that there are other varieties. Torg also speculates that the Outsiders are either people/things that were missed when His Masterness fluxed out the rest of the world, or that they were thrown out of other dimensions into this one. Either way any Outsider (or anyone without a biochip) is considered extremely dangerous and is shot on sight by the REA-5 squads.
The NoFun mutants allied with Crushestro in the main Sluggy universe have been mutated by a scientific squid-on-a-stick. They enjoy pain and call themselves "The Dim-Sum-Henchmen of Pang", which makes them somewhat a parallel to the demons in the Dimension of Pain.