Battle Tripod

Tall. The tripod's body is 30 feet above the ground it stands on if it is not prone. The tripod may choose to lower its body by crouching. Any attack that is aimed at the legs must contend with an armour class of 17, rather than the usual 15.

Long Stride. The tripod can move under and share a space with any creature of size large or smaller. Other creatures of size large or smaller can also move through the tripod's space, but if the tripod is hostile to them then this triggers an opportunity attack from the tripod. The tripod cannot share a space with other creatures if it is prone. If the tripod falls prone, any creatures underneath the tripod must make a DC 13 Dexterity saving throw or take 13 (2d12) bludgeoning damage.

Spiked Limbs. The tripod ignores difficult terrain, and suffers no movement penalty when moving across obstacles up to 15 feet tall. It can wade through water up to 10 feet deep without suffering any movement penalty.

Siege Creature. The tripod deals double damage to objects and structures.

Multiattack. The tripod makes two attacks.

Stomp. Melee Weapon Attack: +9 to hit, reach 20 ft., one target. Hit: 19 (2d10 + 8) piercing damage. Range is measured from the ground underneath the tripod. The tripod cannot use this attack against creatures above its body.

Eye Beam. Ranged Weapon Attack: +9 to hit, range 20/300 ft., one target. Hit: 17 (2d8 + 8) force damage. Range is measured from the tripod's body. 

The tripod has a single legendary action, used at the end of another creature's turn. which it regains at the beginning of each of its turn.

Charge Belly Beam (Costs 1 Action). Targets a point within 300 feet, a bright purple beam of light extending from the tripod's underside to the point being targeted. The tripod cannot move until it takes the Fire Belly Beam legendary action.

Fire Belly Beam (Costs 1 Action).  Can only be used if the previous legendary action was Charge Belly Beam. Must be used at the end of the same creature's turn as the current Charge Belly Beam. All creatures within a 15-foot cube centered on the point  receive 34 (4d10 +12) thunder damage and are Deafened until the end of their next turn. This damage automatically applies to any inanimate objects and structures in the area - the beam is powerful enough to punch a hole through solid rock.

Extra Attack (Costs 1 Action). The tripod makes an attack with either its Stomp or Eye Beam actions.

Spit Fog (Costs 1 Action). The tripod coughs up a gooey ball and spits it to land on a surface within 120 feet. The ball explodes on impact, covering an area around it in opaque fog (a sphere with a 10-foot radius). The area inside the fog is heavily obscured and only creatures with blindsight can see through it. The fog evaporates at the beginning of the tripod's next turn.

Horn (Costs 1 Action). The tripod emits a thunderous low sound, akin to a ship's horn, audible to within 2 miles. All creatures within 100 feet must make a DC 14 Charisma saving throw be become Frightened of the tripod until the end of their next turn. All creatures within 30 feet must make a DC 17 Constitution saving throw or be Deafened until the end of their next turn.