Screaming Skull Catapult
Screaming Skull Catapult is a Tomb Kings war machine that is literally made out of bones. The main framework consists of monstrous creature bones, while human bones are used for reinforcement, with the whole machine bound together by leather straps.
Not only is it made out of bones, but its ammunition are skulls, sand-polished for extra terrifying effect. They scream as they are launched through the air and they explode at impact because of the Undead sorceries. The Undead crew has had centuries of experience, meaning that skulls almost always find their mark.