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While this pet is summoned you will get debuffed and you will have all your resistances reduced by 20. He tints you with a green glow, and makes some mounts and spells look pretty nice.

Drops from the rare NPC Burgy Blackheart. When equipped, it turns you into a Pirate Gnome. While transformed you not only can still mount, but your mounts will be way bigger than one normal gnomes uses.

Drops from Loatheb inside Naxxramas. The pet can be caged and sold in the AH.

Invincible was a horse and an important friend of Arthas. After an injury and without any chances of calling for help, Arthas had to put the horse out of his misery. Years later, now a Death Knight, the horse was risen to serve his master on his dark path.

The mount nowadays only drops from killing the Lich King on Icecrown Citadel 25 man Heroic, and has a really small chance of dropping. With the introduction of the Black Market Auction House, it now have a chance of being sold there. It's one of the most envied mounts ingame.

Murkablo is a mix between a Murloc and Diablo (Main villain from Blizzard's games Diablo I and III). And as the tooltip says, he is the reward from attending to the 2011 Blizzcon (Either online or IRL).

He is a pretty active pet, constantly breathing fire, smoke and walking around.

Varian Wrynn, son of Llane Wrynn and father of Anduin is the current leader of the Alliance and King of Stormwind. He is also called Lo'Gosh, a nickname gave to him by crowds of orcs when he was turned into a gladiator.

Note that this mount isn't Account Wide. Since it Binds to Account, you can mail it to other chars of yours.

Alliance version of the RBG Achievments Reward. It's one of the few mounts in the game that isn't Account Wide. The rewards are the same, but you can mail them to your other characters, even if they don't meet the Achievments criterea.

Reward from Vrykul Archaelogy. It increases you size to the same as Bloodlust/Heroism effects. While buffed you will have a WotLK model helm on your head, regardless if you choose not to show helms on your Interface Options.

It's a nice item since it you don't loose the buff when you mount, and the low CD makes it spammable.