Ancient Basilir Mommy

Petrifying Gaze. If a creature starts its turn within 30 feet of the basilir and the two of them can see each other, the basilir can force the creature to make a DC 16 Constitution saving throw if the basilir isn't incapacitated. On a failed save, the creature magically begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the creature is petrified until freed by the greater restoration spell or other magic.

A creature that isn't surprised can avert its eyes to avoid the saving throw at the start of its turn. If it does so, it can't see the basilir until the start of its next turn, when it can avert its eyes again.

If it looks at the basilir in the meantime, it must immediately make the save. 

Multiattack. The basilir makes two attacks: two with its bite or one bite and one to constrict/swallow 

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 24 (3d10 + 8) piercing damage plus
7 (2d6) poison damage. 

Constrict. Melee Weapon Attack: +12 to hit, reach 5 ft., one Large or smaller creature. Hit: 19 (2d10 + 8) bludgeoning damage plus 17 (2d10 + 8) slashing damage. The target is grappled (escape DC 16) if the basilir isn't already constricting a creature, and the target is restrained until this grapple ends. The Basilir can use his, movement to drag a constricted 10 feet underground each turn, leaving loose earth behind. 

Lightning Breath (Recharge 5–6). The basilir exhales a line of lightning that is 30 feet long and 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 66 (12d10) lightning damage on a failed save, or half as much damage on a successful one.

Swallow. The basilir makes one bite attack against a small 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 behir, and it takes 13 (6d6) acid damage at the start of each of the basilir's turns. A basilir  can have only one creature swallowed at a time.

If the basilir  takes 30 damage or more on a single turn from the swallowed creature, the behir must succeed on a DC 16 Constitution saving throw at the end of that turn or regurgitate the creature, which falls prone in a space within 10 feet of the basilir . If the basilir dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone.