Sphere of Truth

If a white source would deal damage to you, prevent 2 of that damage.

Eight-and-a-Half-Tails

{1}{W}: Target permanent you control gains protection from white until end of turn.
{1}: Target spell or permanent becomes white until end of turn.

Martyr's Cry

Exile all white creatures. For each creature exiled this way, its controller draws a card.

Gideon's Defeat

Exile target white creature that's attacking or blocking. If it was a Gideon planeswalker, you gain 5 life.

Prismatic Strands

Prevent all damage that sources of the color of your choice would deal this turn.
Flashback—Tap an untapped white creature you control. (You may cast this card from your graveyard for its flashback cost. Then exile it.)