The ocean dragon looks terribly weak with such tame health regen and no more mana regeneration. It has virtually no offensive use and is also worse defensively than mountain unless you're just against poke comps. I understand that mana sustain is high in the game but that could be addressed by nerfing Luden's or actually making mana costs matter again, not by making a dragon buff massively unsatisfying.
Don't forget, this regeneration is constant, not just out of combat. In addition, it's possible have 4 of them at once, too.