Early on in the development of Diablo III, Blizzard was subject to heavy criticism about the game's color—in that it had the audacity to contain colorful locations and rainbows. The company responded to the criticism by wearing t-shirts at BlizzCon depicting the game's title in artwork reminiscent of My Little Pony.
Blizzard may have taken it a step further by implementing actual magical ponies into the game, who appear in a secret area much like the Secret Cow Level in Diablo II—which itself was originally spurred by constant rumors that the first Diablo game contained a secret level accessed by interacting with the game's cows.
It's yet to be confirmed by Blizzard, but more enterprising beta testers on reddit who've managed to crack open the game's .MPQ archives found the following details:
A4_1000MonsterFight_Encounter_Name Boss: Battle For Ponies
A4_1000MonsterFight_Taunt_Text The battle for ponies is about to begin.
A4_1000MonsterFight_Join_Instruction {s1} is about to witness
A4_1000MonsterFight_Enter_Instruction You are about to witness
A4_1000MonsterFight_Info_Text The rest of your party will be able to teleport in once you enter
BridlePurpose_Encounter_Name The Pinnacle of Ponies Event
BridlePurpose_Join_Instruction {s1} is about to enter
BridlePurpose_Enter_Instruction You are about to enter
BridlePurpose_Info_Text The rest of your party will be able to teleport in once you enter
