
When another creature you control diesdiesA creature dies when it goes from the battlefield to a graveyard. Being exiled or returned to hand is not dying., transformtransformTo mill a card, put the top card of your library into your graveyard. this creature.
Whenever this creature attacks, return target creature card with mana valuemana valueThe total amount of mana in a card's cost, ignoring colour. A card costing has mana value 4. X counts as 0 except on the stack. 2 or less from your graveyard to the battlefield tapped and attacking.
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Read from the rules text. A card that enables a keyword makes or is the thing; a card that rewards it gets better when you have it. Two cards interact when one enables what the other rewards.