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Adding the Eternamax form to any other tier besides Custom Games means killing them, but since we're talking about a gamemode that's only available through private battle invitations, I don't see why it was removed in the first place. Let people use Eternamax in Custom games, but keep it away...
DNA Donors: Thundurus - Sceptile
Offspring name: Thunduptile
New type:
New base stats: 80(+6)/105(+5)/70(+3)/138(+23)/85(+3)/125(+10) BST: 603
New ability and desc: Wood Art: This Pokemon's Grass-type moves have their priority increased by 1.(Gale Wings clone)
Notable moves: Leaf Storm...