This is a very rare chance when using the https://vanillawowdb.com/?item=7734 Six Demon Bag trinket.

When i was taming a pet, an undead warlock used the Six Demon Bag, and when i fully tamed my pet (Cat) it looked just like the felhound! I asked a GM about it and he said there was no problem in keeping the pet. So where ever i go people always ask where i got it from. It also has manaburn and all the other cat abilities too! Great fro PvP and dungeons becuase it destroys clothies and mana-using beast.

EDIT: Grammar Error

I'm surprised I hadn't before, but has anyone noticed how much these guys resemble the http://us.battle.net/sc2/en/game/unit/zergling zergling units from Starcaft (the original and SCII)? Down to the in-game animation where the dog-like scratching of their ears.

Edited to at the link.