Mr. Bigglesworth is a neutral level 5 house cat belonging to Kel'Thuzad, found just inside the entrance to Naxxramas. Killing him causes Kel'Thuzad to yell:
- Kel'Thuzad yells: No!!! A curse upon you, interlopers! The armies of the Lich King will hunt you down. You will not escape your fate...
- Commander Eligor Dawnbringer says: The last living creature in Naxxramas, this cat is said to be the last thread connecting Kel'thuzad to his mortal life. It is said that any who dare to harm a hair on his head doom themselves to... wait a second, what is he doing on there?
- Commander Eligor Dawnbringer pounds on the display a few times.
- Commander Eligor Dawnbringer says: Well, nevermind. I'm sure no one would be foolish enough to lay a hand on Kel'thuzad's precious pet.
Mr. Bigglesworth in the TCG
- Mr. Bigglesworth will periodically attack the maggots and roaches that meander around the room.
- Despite rumors spread by some players, killing Mr. Bigglesworth has no effect whatsoever on any aspect of the instance.
- The Lil' K.T. vanity pet will kill Mr. Bigglesworth, despite the irony of the situation.
- Mr. Bigglesworth is also the name of Dr. Evil's cat, which starts out as a white persian cat, and ends up a sphinx cat in the Austin Powers series of films.
- Despite being described as the last living creature in Naxxramas by Eligor Dawnbringer, the [Mr. Bigglesworth] battle pet is classified as undead.
- During the final fight with Kel'Thuzad in the Curse of Naxxramas adventure for Hearthstone, if a Hunter uses the Animal Companion spell, they will summon Mr. Bigglesworth instead one of the three usual minions (Huffer, Misha or Leokk). Bigglesworth was also originally planned to be a legendary collectible card in the set.