Legendary Resistance (3/Day).

If Borborygmos fails a saving throw, he can choose to succeed instead.

Poor Depth Perception.

Borborygmos has disadvantage on any attack roll against a target more than 30 feet away.

Siege Monster.

Borborygmos deals double damage to objects and structures.

Actions

Multiattack.

Borborygmos can use his Frightful Presence. He also makes two attacks: one with his maul and one with his stomp.

Maul.

Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 28 (6d6 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 21 Strength saving throw or be knocked prone.

Stomp.

Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 18 (2d10 + 7) bludgeoning damage.

Rock.

Ranged Weapon Attack: +13 to hit, range 30/120 ft., one target. Hit: 29 (4d10 + 7) bludgeoning damage.

Frightful Presence.

Each creature of Borborygmos's choice that is within 60 feet of him and can see or hear him must succeed on a DC 17 Wisdom saving throw or become frightened of him for 1 minute. The frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Borborygmos's Frightful Presence for the next 24 hours.

Legendary Actions

Borborygmos can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Borborygmos regains spent legendary actions at the start of its turn.

Attack. Borborygmos makes a weapon attack.
Bellow (Costs 2 Actions). Borborygmos yells menacingly at one creature he can see within 60 feet of him. That creature must succeed on a DC 17 Wisdom saving throw or become frightened of him for 1 minute. If the creature is already frightened, it becomes stunned instead. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Borborygmos's Bellow for the next 24 hours.
Wide Berth (Costs 3 Actions). Borborygmos moves up to half his speed and can move through the space of any creature smaller than Huge. The first time Borborygmos enters a creature's space during this move, the creature must make a DC 21 Dexterity saving throw. If the saving throw succeeds, the creature is pushed 5 feet away from Borborygmos. If the saving throw fails, that creature is knocked prone, and Borborygmos can make a stomp attack against it.