Legendary Resistance (5/Day). If the beast fails a saving throw, it can choose to succeed instead.

Magic Resistance. The beast has advantage on saving throws against spells and other magical effects.

Siege Monster. The beast deals double damage to objects and structures.

Multiattack. The beast makes five attacks: one with its bite, three with its claws, and one with its tail. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 48 (6d12 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 25). Until this grapple ends, the target is restrained, and the beast can’t bite another target.

Claw. Melee Weapon Attack: +19 to hit, reach 25 ft., one target. Hit: 40 (6d8 + 10) slashing damage.

Tail. Melee Weapon Attack: +19 to hit, reach 25 ft., one target. Hit: 24 (3d6 + 10) bludgeoning damage and 24 (3d6 + 10) piercing damage. If the target is a creature, it must succeed on a DC 25 Strength saving throw or be knocked prone.

Swallow. The beast makes one bite attack against a Huge or smaller creature it is grappling. If the attack hits, the target takes the bite’s damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the beast, and it takes 76 (20d6) acid damage at the start of each of the beast's turns.

If the beast takes 80 damage or more on a single turn from a creature inside it, the beast must succeed on a DC 22 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in an unoccupied space within 20 feet of the beast. If the beast dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 60 feet of movement, exiting prone.

The beast can take 5 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The beast regains spent legendary actions at the start of its turn.

Attack. The beast makes one claw attack or tail attack.

Move. The beast moves up to half its speed.

Chomp (Costs 2 Actions). The beast makes one bite attack or uses its Swallow. 

Quake (Costs 3 Actions). The beast hits the ground with its full weight. Every creature on the ground within 100 feet of the Zillo Beast must make a DC 25 Constitution saving throw or take 35 (7d8) damage and be knocked prone, taking half damage and remaining on their feet on a success.