im not sure. First guess would be that, since eggs and snowballs deal no damage, they dont throw an entity damage event, However, if you look closely, the mobs turn red if you hit them... so my guess is it DOES throw an entity damage event, but the damage is zero (which would allow you to modify it and have them deal damage) So if you want to fire on arrows, your best bet is doing if(event.getDamage()>0){ //code here }