水変化の精体

水変化の精体が戦場に出るか表向きになるに際し、これはあなたが選んだ５/１か１/５になる。
変異{2}{U}（あなたはこのカードを、{3}を支払うことで２/２クリーチャーとして裏向きに唱えてもよい。これの変異コストを支払うことで、これをいつでも表向きにしてよい。）

Aquamorph Entity

As this creature enters or is turned face up, it becomes your choice of 5/1 or 1/5.
Morph {2}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Duel Decks: Speed vs. Cunning

As Aquamorph Entity enters the battlefield or is turned face up, it becomes your choice of 5/1 or 1/5.
Morph {2}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Planar Chaos

As Aquamorph Entity comes into play or is turned face up, it becomes your choice of 5/1 or 1/5.
Morph {2}{U} (You may play this face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

If a creature enters as a copy of a face-up Aquamorph Entity, or a Vesuvan Shapeshifter turns face up as a copy of one, the controller of the creature entering gets to make the choice.

If a creature that's already on the battlefield becomes a copy of a face-up Aquamorph Entity, its power and toughness become the power and toughness that were chosen for the Entity.

The first ability is a replacement effect. The choice is made as Aquamorph Entity is turned face up (or enters); it turns face up (or enters) as a creature of that size. It doesn't become a 0/0 and then a creature of the chosen size.