Titanoboa

If the titanoboa hasn’t eaten a Huge creature in the last 24 hours, it can easily move through any open large enough for a Large creature, and it can squeeze through any opening large enough for a Medium creature. The titanoboa’s destination must still have suitable room to accommodate its volume.

When a creature that can see the titanoboa starts its turn within 30 feet of the titanoboa and the titanoboa is in bright light, isn’t incapacitated, and can see the creature, the titanoboa can force the creature to make a DC 17 Wisdom saving throw. On a failed save, the creature is stunned until the start of its next turn.

Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 30 (5d8 + 8) piercing damage.

Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 30 (4d10 + 8) bludgeoning damage, and the target is grappled (escape DC 18) if it is a Huge or smaller creature. Until this grapple ends, the target is restrained, and the titanoboa can't Constrict another target.

The titanoboa makes two Bite attacks or one Bite attack and one Constrict attack. It can replace one Bite attack with a use of Swallow.

The titanoboa makes one Bite attack against a Huge or smaller target it is grappling. If the attack hits, the target is also swallowed, and the grapple ends. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside the titanoboa, and it takes 21 (6d6) acid damage at the start of each of the titanoboa's turns. If the titanoboa takes 30 damage or more on a single turn from a swallowed creature, the titanoboa must succeed on a DC 15 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the titanoboa. If the titanoboa dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 20 feet of movement, exiting prone.