- Mega Cloyster - Mega Seviper - Mega Zangoose - Mega Spiritomb - Mega Ninetales - Mega Banette - Mega Sableye - Mega Rotom - Mega Rapidash - Mega Arcanine - Mega Ariados - Mega Musharna - Mega Gigalith - Mega Scoliopede - Mega Cofagrigus - Mega Reuniclus - Mega Klinklang - Mega Cryogonal - Mega Volcarona
Mega Cryogonal... now that you mention it. With an increase in defense and HP it could be a decent pokemon.
I don't think there will ever be a form change/mega evolution that changes HP, since it would cause some calculation issues. --- Official Mike Meekins of AA5 boards. Official Olimar of SSB Wii U Boards. Playing: Mega Man 8, Okami HD, Pokemon Black 2