Unusual Nature.

The eel doesn't require air.

Actions

Multiattack.

If it isn't attached to a creature, the eel makes one Bite attack and one Tail Spine attack.

Bite.

Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 4 (1d6 + 1) piercing damage, and the eel attaches to the target. While attached, the eel can't make Bite attacks. Instead, the target takes 4 (1d6 + 1) piercing damage at the start of each of the eel's turns. The eel can detach itself as a bonus action. A creature, including the target, can use its action to detach the eel.

Tail Spine.

Melee Weapon Attack: +3 to hit, reach 5 ft., one creature. Hit: 3 (1d4 + 1) piercing damage, and the target must succeed on a DC 10 Constitution saving throw or be poisoned for 1 minute. Until this poison ends, the target is paralyzed. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Space Eel