Great Wroggi, Poison Wyvern

If Great Wroggi, Poison Wyvern dealt combat damage to a creature with a +1/+1 counter on
it, remove a +1/+1 counter from that creature. Then put that many +1/+1 counters on Great Wroggi, Poison Wyvern.

As long as Great Wroggi, Poison Wyvern is on the field, all other Great creatures you control get +1/+1.