I'm willing to bet there was a certain amount of ambient psychic energy in the air from new and mewtwo fighting. Given that the psychic energy is what turned him to stone in the first place, the dramatic shift in emotion caused a dramatic shift in him being made of stone. Couple that with both m&m2 who turned him to stone in the first place no longer desiring violence could have changed him back.
Come to think of it, were the tears ever explained?
Something, something, friendship.
I'm willing to bet there was a certain amount of ambient psychic energy in the air from new and mewtwo fighting. Given that the psychic energy is what turned him to stone in the first place, the dramatic shift in emotion caused a dramatic shift in him being made of stone. Couple that with both m&m2 who turned him to stone in the first place no longer desiring violence could have changed him back.