You can upgrade Clanrat and Stormvermin units to include a single weapon team. Warpfire throwers, manufactured by clan Skyre, and sold to the other clans. They combine technology similar to the dwarf flame cannon combined with warpstone, which makes for a smaller, very destructive, if slightly dangerous war machine. The Warpfire Thrower kit makes 1 model. Note that a variety of designs are available and are supplied at random.