Lifelink. Whenever the harpy deals damage with one of its attacks, it regains hit points equal to half the amount of damage dealt. 

Diseased Form. The harpy has advantage on saving throws against being poisoned. Additionally, whenever the harpy hits a target with a natural melee weapon attack (non-club), the target, if a creature, it must succeed on a DC 12 Constitution saving throw or contract a disease. Until the disease is cured, the target can't regain hit points except by magical means, and the target's hit point maximum decreases by 3 (1d6) every 24 hours. If the target's hit point maximum drops to 0 as a result of this disease, the target dies.

Multiattack. The harpy makes two attacks: one with its claws and one with its club or bite.

Claws. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 6 (2d4 + 1) slashing damage.

Club. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 3 (1d4 + 1) bludgeoning damage.

Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 1) piercing damage.

Luring Song. The harpy sings a magical melody. Every humanoid and giant within 260 feet of the harpy that can hear the song must succeed on a DC 11 Wisdom saving throw or be charmed until the song ends. The harpy must take a bonus action on its subsequent turns to continue singing. It can stop singing at any time. The song ends if the harpy is incapacitated.

While charmed by the harpy, a target is incapacitated and ignores the songs of other harpies. If the charmed target is more than 5 feet away from the harpy, the target must move on its turn toward the harpy by the most direct route, trying to get within 5 feet. It doesn't avoid opportunity attacks, but before moving into damaging terrain, such as lava or a pit, and whenever it takes damage from a source other than the harpy, the target can repeat the saving throw. A charmed target can also repeat the saving throw at the end of each of its turns. If the saving throw is successful, the effect ends on it.

A target that successfully saves is immune to this harpy's song for the next 24 hours.