Martyr of Frost
Creature — Human Wizard
, Reveal X blue cards from your hand, Sacrifice this creature: Counter target spell unless its controller pays 
.
Wayne England
Salvat 2005 (PSAL)
• #H5Rulings
A card that’s already revealed for another cost or because of an effect can be revealed to pay this cost.
(wotc • 2006-07-15)
Each card that’s revealed to pay the cost remains revealed until the ability leaves the stack.
(wotc • 2006-07-15)
If one of the cards that’s revealed to pay the cost leaves its owner’s hand before the ability resolves, it stops being revealed, but the value of X is not affected.
(wotc • 2006-07-15)
Rulings
A card that’s already revealed for another cost or because of an effect can be revealed to pay this cost.
(wotc • 2006-07-15)
Each card that’s revealed to pay the cost remains revealed until the ability leaves the stack.
(wotc • 2006-07-15)
If one of the cards that’s revealed to pay the cost leaves its owner’s hand before the ability resolves, it stops being revealed, but the value of X is not affected.
(wotc • 2006-07-15)