Cannon From Daldana

Break Through. If the Cannon destroys a tower / wall / gate; any enemy creature must throw a 13 WIS save: On fail they have disadvantage on their next roll. Any ally to the Cannon become inspired by 1d4 for their next roll.

Bulldoser. The Cannon's bludgeoning damages are doubled against buildings and constructs, natural barriers.

Buildup:

Barrier. 70 HP, 16 AC. Its the outer layer with immunities and resistances that the whole construct has. If you break through the barrier choose to focus on these targets below:
1. Drivers. The Cannon is leaded by 2 mechanics inside. They also covered by an another harder shield that has 30 HP, 18 AC  The inner-shield is made of mithral, has resistance against non-magical attacks.. The inner barrier has resistance to any kind of damage.
Each of the drivers are humanoids and has 15 HP, 13 AC. While they drive they need to concentrate, otherwise the Cannon stops its actions.
2. The Cannon. The Cannon has a magical cannon that it makes its attacks with: It is uncovered by the Barrier, but still has 70 HP, 18 AC. The cannon is made of mithral, has resistance against non-magical attacks.

To Drive the Cannon: Drivers can not do other actions than lead the machine. Its necessary to spend 1 action to get inside the drive panel, also 1 to leave that. Until then the user is restrained to the chair. Drivers must succeed a 8 DC INT check before make any kind of action with the Cannon. If any of them fails, the action won't happen. Drivers have half-cover inside the Cannon if the barrier is broken, full cover until its not.

Cannon. (One action to reload, 1 to shot) Magical, Ranged Weapon Attack: range: 60 - 800 ft. The shots hit all creatures and objects in a 30 ft. Circle within range. Hit: 15 (1d20 +5) fire damage + 20 (3d10 +5) bludgeoning damage. Count down the value of creature's DEX save of the full damage; Do a 15 STR save, otherwise fall on the ground prone. For this DEX save all creatures has advantage on their rolls.

Inaccurateness: Roll an 1d20: If the roll is
1-5; the strike is inaccurate; lands in 30 ft. from the desired point.
6-14; the strike is halfway to be accurate; lands in 15 ft. from the desired point.
15-20; the strike is accurate; hits the desired point.
If the shoting range is longer than 400 ft, count down -5 from the rolled value / every 100 ft.

Battering Ram (One action). Melee Weapon Attack: +7 to hit; Reach: 20 ft. one target, only against walls, buildings, natural barriers. Hit: 30 (2d20 + 10) bludgeoning damage.

Crushing. (Movement, non-action) If the Cannon drives through a creature this creature must throw a 13 DC DEX save or takes 9 (3d6) bludgeonging damage. Also 15 STR or become grappled under the Cannon. (Escape DC is a 15 STR.) If a creature starts it turn under the Cannon takes this damage again. 

Flamethrower (Bonus Action). Ranged Weapon Attack: +5 to hit; Reach: 0-15 ft. any target within range that stays in front of the Cannon. Hit: 9 (1d8 + 5) fire damage.