I literally recommend orange dream and enchi to everyone who asks about what to breed a snake to but other then that a blue eyed Lucy would be really nice I think. That way every snake you produce would either be another blue eyed Lucy or a mystic potion. Another possibility would be a crystal which would let you produce 25% crystals, 25% blue eyed Lucys 25% mystic potions and 25% mystic crystals. It really depends on what you like.