虚空魔道士の弟子

変異 {2}{U}{U} （あなたはこれを、{3}を支払うことで、裏向きの２/２のクリーチャーとして唱えてもよい。 いつでも変異コストを支払ってそれを表向きにすることができる。）
虚空魔道士の弟子が表向きになったとき、呪文１つを対象とし、それを打ち消す。

Voidmage Apprentice

Morph {2}{U}{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 this creature is turned face up, counter target spell.

Duel Decks Anthology: Jace vs. Chandra

Morph {2}{U}{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 Voidmage Apprentice is turned face up, counter target spell.

Duel Decks: Jace vs. Chandra

Morph {2}{U}{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 Voidmage Apprentice is turned face up, counter target spell.

Legions

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.

If a spell with split second is on the stack, you can still respond by turning this creature face up and targeting that spell with the trigger. This is because split second only stops players from casting spells or activating abilities, while turning a creature face up is a special action.