Endurance of Ancients

Creatures you control have survival. (At the
beginning of each end step, if a creature you control
was dealt damage this turn, put a +1/+1 counter on
it. If a creature has multiple instances of survival,
each triggers separately.)
Whenever you put one or more +1/+1 counters
on a creature, you may pay {r/g}{r/g}. If you do, put
an additional +1/+1 counter on that creature.