Stonekeeper's Oath

When Stonekeeper's Oath enters the battlefield,
you may search your library and/or graveyard for
a card named Time Stone, reveal it, and put it
into your hand. If you search your library this
way, shuffle it.
Sacrifice Stonekeeper's Oath: Prevent all damage
a source of your choice would deal this turn.
We swore an oath to protect the
Time Stone with our lives.