Slave Knight Gael

This spell costs {1} less to cast for each creature that
died this turn.

Whenever another creature dies, Slave Knight Gael
gets +1/+1 until end of turn. If that creature was
legendary, put a +1/+1 counter on it instead.

Whenever Slave Knight Gael attacks, it deals X
damage to up to X target creatures, where X is
equal to the number of +1/+1 counters on it.