Gargos is a portal character. According to forum and canon lore, portal characters don’t need a stage since they are invading from a portal. In KI lore, portals don’t work both ways, so only gargos can utilize a portal to come on over, but that same portal can’t be used to travel back by anyone other than gargos. He probably has it equipped with a retinal scanner made special for demon purple eyes.
Hence why Rash doesn’t have a stage either, he’s from a portal and coming on over. His portal however has a digital tounge scanner instead.
Arbiter does get a stage because he’s from M-SoftGates land, the real world place where a race of aliens created the actual tournament and financed it, all while confusing Aria into thinking she was the one that is running the show.