Advantages over Purify:
It's a creature, so it's useful for 3 or 5 damage even against non-poison decks.
It has purify ability, so you can remove poison multiple times with 1 card.
Personally, I would probably use this mount upgraded, since it has a high attack compared to the other mounts, is cheaper compared to other mounts, and almost guarantees a victory against poison decks, but that's just my take on it.
What changes should I make, other than changing the ability, that would make you want to use this card?