Brewfest Kodo

This mount can not be obtained/learned as of now, instead your mount transforms into this if you ride a 60% mount* when you use [item=37750] as Horde, or [item=39476] as Alliance, these cost 2 or 5 [item=37829]s respectively and are of course only available and useable during Brewfest (though Horde characters can obtain [item=37816] for 20 tokens which don't disappear after Brewfest)

* that was pre-4.0, haven't checked yet how the scaling affects this afterwards, presumably you only see the "slow" versions if you don't have 100% Riding yet.

Seems this got added to the Official WoW Armory, new Companions and Mounts Section, it shows Not Collected yet for this 1, for me.

This is one of the mounts on the offical WoW armory that has currently never been implemented into the game.
In the table below I've listed all the mounts that appear on the WoW armory but have never been implemented into the game, patch indicates the patch it was datamined.

Mount

Patch

Illidari Doomhawk

3.0.3

Black Polar Bear

3.0.3

Black Riding Yak

5.0.4

Blue Qiraji War Tank

7.3.5

Modest Expedition Yak

5.0.4

Gray Wolf

?

Brewfest Kodo

3.0.3

Red Qiraji War Tank

7.3.5

Riding Kodo

2.4.3

[spell=302796]

8.2.0

[spell=302794]

8.2.0

[spell=239363]

7.2.0

[spell=302795]

8.2.0

[spell=302797]

8.2.0

[spell=194046]

6.2.1

Tiger

3.0.3

Kafa Yak

5.0.4

[npc=359]

?

Grand Caravan Mammoth

3.0.1