Ballista

Armor Class: 16
Hit Points: 40
Damage immunities: poison, psychic
Like the crossbow, except bigger and mounted on a stand.
Before it can be fired, it must be loaded and aimed. It takes one action to load the weapon, one action to aim it, and one action to fire it.
Ballista Shot: Ranged Weapon Attack: +6 to hit, range 100/300 ft, one target. Hit: 26 (3d12+9) piercing damage.