残響の追跡者

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。）
残響の追跡者が表向きになったとき、クリーチャー１体を対象とし、それをオーナーの手札に戻す。

Echo Tracer

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.)
When Echo Tracer is turned face up, return target creature to its owner's hand.

The List

Duel Decks: Speed vs. Cunning

Legions

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.)
When Echo Tracer is turned face up, return target creature to its owner's hand.

The trigger occurs when you use the Morph ability to turn the card face up, or when an effect turns it face up. It will not trigger on being revealed or on leaving the battlefield.