How do I have 601 Total Pets while having 379 Unique Pets and NO duplicates?! Then I thought: if I were a programmer at Blizzard with a ton of stuff to do, what would I do to give PTR players "random" pets?
I'd make it give the player 50 number of random pets between SpeciesID 1 and SpeciesID 1400. The thing is that about 1/2 or so one of those SpeciesIDs don't exist... but for the Total and Unique amounts to be different, some of them must exist (for example, tamer pets).
However, the problem is that there is no way to look for these "pets that don't exist but must exist" within the game. The API allows you to look up pets by Index (i.e. the order in your Journal, and these pets are not in the Journal), Species (but it doesn't tell you the PetID, so you can't know if you own it), and PetID (a 16 digit hexadecimal string).
I realized that PetIDs must be sequential on the PTR because the pets are all given to you at the same time on the PTR (when you log in). Therefore, I wrote an addon that finds the PetID of all pets in your Journal, then marks them as "found" and tests for the existence of "Pets that don't exist but must exist" at all PetID values within a range of +/- 3 of the "real" PetIDs. By systematically searching like this, I found what I was looking for.
So, if you want to screw around with pets that should not exist, here's the addon I made ("SekritPets"): http://www.mediafire.com/?tdpztddja95oxdi
I don't have it hosted on a more official source this is an addon that only matters for the PTR and it seems silly to use Curse for something like that (but I might if there is interest).
Don't bother unless you are on the PTR.
Firstly, do "/sek" to generate a list of all the "secret" pets you have in chat.
Next, you can use "/sek summon" (and then link the pet into the chat message) to summon the pet you linked.
You can use "/sek setX" (and then link the pet into the chat message) to set the linked pet to X slot in your active pet team (X can be 1-3).
Additionally, you can do "/sek tamer" to generate a list of all the "tamer" pets you have.
Lastly, you can use "/sek bof" to generate a list of all of the new Beasts of Fable that you have. These are the legendary "boss" pets (that are meant to be fought 1v3). They're fun to screw around with.
Some fun examples so far
Don't you wish we had an Undead Murloc pet with a glowing light on its head and the abilities Reckless Strike and Wish?
Good sir Lucky Yi, I'm sorry to inform you, but we have you outnumbered. (Yi is a Beast of Fable, so I brought 3.)