Catapult

Monster's CR. Depending on what the DM comes up with the CR is up for interpretation. Use your judgement of what the actual CR is, this is a baseline for rules and up you to customize at your leisure.

Siege Machine Operators. This is an inanimate object therefore must be operated by men and/or women who know how to use it. There must be at least 3 Siege Machine Operators for the Catapult to be used. There are normally 3-5 Siege Machine Operators that work the Catapult. When operating the Catapult all of the Siege Machine Operators must use their actions as one (no matter how many) and are automatically are using their action to "use object" to operate the Catapult. The NPCs listed below are some examples of who the DM can use as Siege Machine Operators.

• Novices: Guard, in the Basic Rules.
• Skilled: Soldier, in the Guildmasters' Guide To Ravnica.
• Expert: Veteran, in the Basic Rules.

 Siege Machine Operator Skill. There are 3 skill levels of the Siege Machine Operators.

• Novices. Novices are unskilled users of this siege machine. When the Fire action is taken roll a percentile die. If rolled 50% or lower, add a -10 to the To Hit modifier for that Fire action.
• Skilled. Skilled users have been in regular use of the siege machine. When the Fire action is taken roll a percentile die. If rolled 25% or lower, add a -5 to the To Hit modifier for that Fire action.
• Experts. Expert users of this siege machine know it's every nook and cranny. The experts have used the Catapult so much that they use the catapult with no issue.
• Percentages. Percentile die + d10.  Examples: 50 + 1 = 51; 00 + 1 = 1; 00 + 0 = 100

Ammunition. There are many types of ammunition to be used with a catapult, it is up to the DM what type of ammunition is used. Most commonly used is boulders but anyone who uses it can get creative. Some examples are listed below.

• Boulder. 3d12 Bludgeoning Damage; The basic and most effective ammunition used to knock down walls when attacking settlements.
• Fire Stone. 1d12 Bludgeoning Damage,  2d12 Fire Damage; A large stone not as large as a boulder but covered in hay woven around the stone itself to create a ball. It is then lit on fire with a combustible liquid. Effective when used to burn down wooden buildings.
• Skeletal Swarm. 2d8 Slashing Damage; A skeletal swarm is a swirling mass of bones that is formed together by dark energy from a Necromancer. This type of ammunition is used by undead armies to quickly sew chaos on the battlefield. After this ammunition lands on the target there is a Skeletal Swarm at the point of impact. Skeletal Swarm is in the Ghosts of the Saltmarsh.

Make of the Catapult. The make of the catapult determines how durable it is to receiving damage. This is up to the DM's discretion of what the Catapult is made of. These are some examples that can be used.

• Cobbled Make. AP 16, Full HP: 24 (2d12) A poorly made Catapult, commonly made with spare wood, unfinished logs and common rope.
• Fine Make. AP 18, Full HP: 48 (4d12) A well made Catapult made with finely manufactured wood and treated ropes to make the Catapult durable to both the elements and to enemies.
• Metal Make. AP: 20, Full HP: 96 (8d12) A Catapult of this make is rarely made. It is incredibly resilient and made of pure metal. Even the ropes are of cables braided together.

Inanimate Object.  Has Disadvantage to Dexterity Saving throws since it cannot react to anything. If there are any other rules regarding certain spells being cast on the Catapult it is up to the DM to decide the correct ruling.

Fire. When loaded the Siege Machine Operators can fire the catapult. After firing the Catapult the Siege Machine Operators must take the Reload action with the Catapult to be able to Fire again. Ranged Weapon Attack: +10 to hit, range against structures 500/1000 ft., against non-structures on the ground 150/300 , Hit:  +10 Example Ammunition: Boulder (3d12 + 10) Bludgeoning damage.

Reload. After the Catapult has taken the Fire action the Siege Machine Operators must take the Reload action to be able to Fire again. The Catapult is promptly reloaded to be fired again.