
Whenever 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., you get an experience counter.
At the beginning of your end step, choose target creature card in your graveyard. If that card's 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. is less than or equal to the number of experience counters you have, return it to the battlefield. Otherwise, put it into your hand.
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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.