Full patch notes are here

[Alice_89th]

Earth pony + wind pony + water pony + fire pony + heart pony = captain planet pony

What, no Rainbow Dash?
Or Nyancat

Tank Achievement mounts
But Somebody's Gotta Do It (Paladin) Complete 200 high-level full party duties as a paladin. Item: Warlion Horn
But Somebody's Gotta Do It (Warrior) Complete 200 high-level full party duties as a warrior. Item: Warbear Horn

You actually have to tank 200 parties. So much for those people who said they would just level tank for the mounts.

That was the idea, a reward for those who have been tanking for a long time.