Senesca, Magisterial Reject

Senesca, Magisterial Reject enters the battlefield with X blood counters on it, where X
is the amount of life paid to cast this spell.
Remove a blood counter from Senesca, {t}: put
two -1/-1 counters on target creature. Then, if Senesca has no blood counters on it, sacrifice Senesca, Magisterial Reject.
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"My last will.. is your demise.."