Scalpel Leech

The leech has advantage on attack rolls against any creature that doesn't have all its HP.

The leech can breathe air and water.

Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 1 piercing damage, and the leech attaches to the target. While attached, the leech doesn't attack, and at the start of each of its turns the target takes 4 (1d4+2) necrotic damage and must succeed on a DC 11 Constitution saving throw or contract the weeping plague (a magical disease; while diseased the target gains one level of exhaustion that can't be removed until the disease is cured). A creature can detach the leech with a successful DC 12 Strength check as an action.

The leech moves up to its speed without provoking opportunity attacks.