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Open map.cpp. Goto the very end of Map::Attack(blah). Right before the last bracket add:
if (from->player->character->paperdoll[Character::Weapon] == ID)
{
    UTIL_PTR_VECTOR_FOREACH(this->npcs, NPC, closenpc)
    {
        int dist = util::path_length(target_x, target_y, closenpc->x, closenpc->y);
        int dmg = util::rand(from->mindam, from->maxdam);

        if (distance <= 6 && closenpc->alive)
        {
            PacketBuilder eff;
            eff.SetID(PACKET_EFFECT, PACKET_AGREE);
            eff.AddChar(closenpc->x);
            eff.AddChar(closenpc->y);
            eff.AddShort(ID);

            from->player->character->SendBuilder(eff);
            closenpc->Damage(from, dmg);
        }
    }
}