Senna, The Redeemer

Whenever a token creature you control dies you
get an experience counter.
{2}{w}{b}{t}: Dawning Shadow— Choose X target creatures, where X is the number of experience counters you have. Chosen creatures you control
gain hexproof until end of turn. Tap chosen creatures your opponents control, Senna then
deals damage equal to the number of creatures
tapped with this ability to creatures tapped with
this ability. You gain 1 life for each creature that
dies from this ability.