Dipsa

Amorphous. The dipsa can move through a space as narrow as 1 inch wide without squeezing.

Discreet Bite. The bite of a dipsa is barely perceptible and the wound is quickly anesthetized. When the dipsa hits with a Bite attack, the target must succeed on a DC 15 Wisdom (Perception) check to notice the dipsa and its attack. Each time the creature takes acid damage from an attached dipsa, it can repeat this check, noticing the dipsa on a success. A creature that takes acid damage from the dipsa while below half its hp maximum automatically succeeds on this check.

Ooze Nature. The dipsa doesn't require sleep.

Swamp Camouflage. The dipsa has advantage on Dexterity (Stealth) checks made to hide in swampy terrain.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 1 piercing damage, and the dipsa attaches to the target. While attached, the dipsa can't attack, and at the start of each of the dipsa's turns, the target takes 3 (1d6) acid damage and must succeed on a DC 12 Constitution saving throw or have its hp maximum reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hp maximum to 0.

Translucent. The dipsa takes the Hide action.