My Rivnak is pet 1, and I can always summon and dismiss him with "/pet 1,"
"/pet 0, summon" has always gotten me a message about the ring being depleted. How do I "undeplete" it? Judging by the fact that it seems to acknowledge that pet 0 is there (/pet 0 dismiss tells me he's already in the netherworld), and that I "don't have a pet called 2", I guess I do have another pet, I just can't ever call it.