
Whenever this creature attacks, you may sacrifice another creature. If you do, put a number of +1/+1 counters on this creature equal to the sacrificed creature's power.
When this creature diesdiesA creature dies when it goes from the battlefield to a graveyard. Being exiled or returned to hand is not dying., amassamassPut X +1/+1 counters on an Army you control. It's also a Goblin. If you don't control an Army, create a 0/0 black Goblin Army creature token first. Goblins X, where X is this creature's power. (Put X +1/+1 counters on an Army you control. It's also a Goblin. If you don't control an Army, create a 0/0 black Goblin Army creature token first.)
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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.