msem-instigator

Improve {R} ({R}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
Whenever Galdurheim Reaver attacks, it deals damage to the player or planeswalker it's attacking equal to the number of embattled creatures you control. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)