You can discard 4 other "Mermail" monsters in your hand to the Graveyard; Special Summon this card from your hand. When you do: Target cards your opponent controls, up to the number of "Mermail" monsters in your Graveyard (if possible); this card gains 500 ATK, and if it does, destroy those targets (if any). You can Tribute 1 other face-up Attack Position "Mermail" monster; this card gains the following effect this turn.
At the start of the Damage Step, if this card battles a Defense Position monster; Destroy that monster.
A new forme to me is rather silly I suppose I can understand them not using it for the LGFR manga when Deoxys overpowered Mewtwo for a time (Red turned the tables in Mewtwo's favour to beat Deoxys) but I don't understand how a Genetic Pokemon that has no forme changes for as long as Mewtwo suddenly gains one, basically this should have been done years ago, maybe LGFR generation or HGSS time.
Basically I'm not a fan, because this should have been done years ago, not now.