Somehow, I would have believed that this card would have a "you win" effect, rather than the current "all ponies": "You win the game if you control six or more legendary pony tribal enchantments or six or more legendary pony creatures". Believe it or not, the card would not be overpowered: I was a user of Coalition Victory for the longest time, and it was a pain to use. Here, the bar is so hard that even a dream game would have a hard time using this win condition before turn 8-10. Furthermore, after cards like Omniscience and Blightsteel Colossus, the word OP has lost most of its meaning in Magic.
At that, I would also mention that I think the various Elements should be labeled "Legendary Tribal Enchantment: Pony".