Armiventem

Soft Underbelly. If the armiventem is knocked prone, it takes a -3 to AC.

Strong Stomach. Any damage to the armiventem caused from within it's stomach is reduced by half

Multiattack. The armiventem makes two claw attacks, then one tongue attack, then one rolling attack.

Claw Attack. The armiventem slashes at an enemy with it's claws.

Claw Melee Attack. Melee Weapon Attack: +10 to hit, reach 10 ft., 1 target. Hit: 28 (4d10 + 6) slashing damage.

Rolling Attack. The armiventem lunges forward while curling up into a ball and rolling forward. Anyone in the area of effect must make a DC 17 dex save. Full damage on a fail and half on a success.

Rolling Melee Attack. Melee Weapon Attack: +10 to hit, reach 50 ft., all targets in a 10ft wide path.. Hit: 33 (5d10 + 6) bludgeoning damage.

Tongue Attack. The armiventem uses it's long tongue to grab one enemy and bring them closer.

Tongue Melee Attack. Melee Weapon Attack: +10 to hit, reach 50 ft., 1 target. Hit:  11 (2d10 + 6) bludgeoning damage.

A medium or smaller creature hit by the armiventem's tongue is brought within 5ft of the armiventem and is grappled by it. On the creature's turn, it may choose to break out of the grapple with a successful str contest against the armiventem. If a creature is knocked unconscious by this attack, the armiventem can swallow it immediately. Otherwise, it may take the swallow action on it's next turn.

Swallow. The armiventem makes one tongue attack against a medium or smaller creature it is grappling. If the attack hits, the target takes the tongue attack'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 armiventem, and it takes 21 (6d6) acid damage at the start of each of the armiventem turns.
If the armiventem takes 30 damage or more on a single turn or 60 damage or more in a single round from the creature(s) inside of it, the armiventem must succeed on a DC 15 constitution saving throw at the end of that turn/round or regurgitate all swallowed creatures, which fall prone in a space within 5 feet of the armiventem. If the armiventem dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone. If the armiventem takes the swallow action, it may do another attack.