Prominence of the Exemplar

Whenever a creature you control with a great
coun attacks alone, it gets +2/+3 until end of turn
When Prominence enters the battlefield, put a
great counter on a creature you control.
Creatures you control with great counters on
them have indestructible.
When a creature you control with a great counter
dies, put a -1/-1 counter on each creature you
control and you lose 3 life.
If you control no permanents with great counters
on them, sacrifice Prominence.