Insatiable Goldblade

Insatiable Goldblade has backstab X, where X is
its power. (If this creature would deal combat
damage to an opponent, you may put X -1/-1
counters on a creature that player controls instead.)
Whenever a creature an opponent controls with
a -1/-1 counter on it dies, put a +1/+1 counter on Insatiable Goldblade and you lose 1 life.
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An unquenchable thirst.