Serpentine Spirit

The serpent can hold its breath for 15 minutes.

The serpent has advantage on Wisdom (Perception) checks.

The serpent's bite attack deals an extra 1d6 + summonSpellLevel poison damage. Once per turn, when it hits with a bite attack, you can force the target to make a Constitution saving throw against your spell save DC or be poisoned for 1 minute. It can repeat the Constitution saving throw at the end of its turns, ending the effect on a success.

The serpent makes a number of attacks equal to half this spell's level (rounded down).

Melee Weapon Attack: your spell attack modifier to hit, reach 5 ft., one target. Hit: 1d6 + 2 + summonSpellLevel piercing damage.

Melee Weapon Attack: your spell attack modifier to hit, reach 5 ft., one target. Hit: 1d8 + 2 + summonSpellLevel bludgeoning damage, and the target is grappled (your spell save DC to escape). Until this grapple ends, the creature is restrained, and the snake can't constrict another target.

The serpent lifts its upper body up, flaring out its neck like a hood and hissing menacingly. Each creature of your choice that is within 30 feet of the serpent and can hear it must succeed on a Wisdom saving throw your spell save DC or become frightened of the serpent for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

The serpent makes one bite attack against a Medium 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 serpent, and it takes 1d12 + summonSpellLevel acid damage at the start of each of the serpent's turns. The serpent can have only one creature swallowed at a time.

If the serpent takes 30 damage or more on a single turn from the swallowed creature, the serpent must succeed on a DC 12 Constitution saving throw at the end of that turn or regurgitate the creature, which falls prone in a space within 10 feet of the serpent. If the serpent dies, a swallowed creature is no longer restrained by it and falls prone as the serpent disappears.