445 pets
Vampiric Batling
(70.4%)
Binds when picked up
Use: Teaches you how to summon this companion.
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Neutral
Flutters about.
Wing flutter (constant); vocalizations (on-click)
This pet had a 100% chance to drop from Tenris Mirkblood, a temporary elite raid boss. The quest Chamber of Secrets leads players to this mob, although players did not need the quest to fight him. This boss was only available during the Scourge Invasion event leading up to the launch of Wrath of the Lich King. The window of opportunity to obtain this pet was about 3 weeks.
Tenris Mirkblood was found in Karazhan in the previously locked Servant's Quarters located up the stairs just past Attumen the Huntsman. It took a raid group of between 5 and 10 players to bring him down. Note that ALL players in the raid were able to loot this pet.
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Dragonkin
Just when the scourge was driving me batty, along comes this little fellow, and I don't even have to win a roll! You must have bats in your belfry if you don't rush over to Karazhan to snag this guy for yourself. And watch out for zombies along the way. They're often lurching about where you least sus— *choke* Braaaaaiiins!!! *nom nom nom*
When this pet was available I wasn't high enough yet to go on the boss fight; I had just been introduced to WoW a few months before. I'm the one who told my guildies about it though and they all got one. I'm hopeful that some day I will be able to add it to my collection.. Please, Blizz.. give us poor shleps who missed out a second chance!
I am one of the lucky few who got this pet. None of us knew it existed and did the raid just for the new event boss. Then low and behold we each got the pet, and I won the Arcanite Ripper XD
The report that the Vampiric Batling has been seen on BMAH was probably somebody mistaking it for the Tirisfal Batling, it is unlike blizzard to make event pets available outside of the event. I am also in the boat that I was unable to collect this pet :(
This was one of the first trio of pets I got up to 25 (it was paired with a panther cub and a sinister squashling), and it remains one of the pets I use as a go-to for tough pet battles due to the fact that it's undead (so you're guaranteed at least two rounds even if the other pet goes first and one-shots you, as long as you aren't stunned) and has a high-damage ability in Reckless Strike.
Even with pet battles out it's still not tradeable, sad panda moment.
Although this pet is not cage-able in the Mists expansion, there are rumors that it has been seen in the Black Market Auction House. If you've got the dough (bids start at ~20k, no buyout, no limit) you may just be lucky enough to get a second chance. (The Arcanite Ripper is also on the list of possible items!)