So if I have a Mamoswine that has a Memory Berry attach to it and use Piloswine's Rouse does it add damage and heal 40 hp or does it just do 20 damage because it states damage on Piloswine?
Whenever a Pokemon attack references itself, and another Pokemon uses it, replace that species' name with 'this Pokemon'. So you would deal 20+10 for each damage counter, then remove 4 damage counters from Mamoswine.