Bouldai Lizard v2.1

Earth Glide. The lizard can burrow through nonmagical, unworked earth and stone. While doing so, the lizard doesn't disturb the material it moves through

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

Multiattack. The lizard makes two attacks: one with its bite and one with its tail. One attack can be replaced by Swallow or Rollout.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) piercing damage, and the target is Grappled (escape DC 15). Until this grapple ends, the target is Restrained, and the lizard can’t bite another target.

Tail. Melee Weapon Attack: +7 to hit, reach 10 ft., one target not Grappled by the lizard. Hit: 12 (2d6 + 5) bludgeoning damage. If the target is a creature, it must succeed on a DC 15 Strength saving throw or be knocked Prone.

Swallow: The lizard makes one bite attack against a Medium or smaller target it is Grappling. If the Attack hits, the target is swallowed, and the grapple ends. The swallowed target is Blinded and Restrained it has total cover against attacks and other Effects outside the lizard, and it takes 10 (3d6) acid damage at the start of each of the lizard's turns. The lizard can have only one target swallowed at a time.
If the the lizard dies, a swallowed creature is no longer Restrained by it and can escape from the corpse using 5 feet of Movement, exiting prone.

Rollout. Melee Weapon Attack: +7 to hit, reach 10 foot line., each creature in the line. Hit: 16 (2d10 + 5) piercing damage, the target is knocked prone. Each turn the lizard uses this attack against the same target that it used the attack against the last turn the damage of the attack is increased by 1d10 if the attack hits.