I dont really get the point of Ice Beam being a move with slashes. It hits most of the Dragons in the tier for supereffective damage. Without Ice Beam, Zekrom can take a hit and hit it back. Lugia and Giratina and Giratina-O and even Groudon, to an extent, can prove to be even more problematic. Fire Blast needs a slash with Aura Sphere and just a mention that Mewtwo should use Fire Blast if it has Drought support since a Sun-Boosted Fire Blast is as strong as a supereffective Aura Sphere. So, the point about hitting Dialga and Steel-Arceus with Aura Sphere is not that important. Also if Mewtwo is used in a sun team then it will have very little use for Aura Sphere since all that it needs to hit will be dealt the same damage from sun-boosted Fire Blast.