Beatle

Shapechanger. The doppelganger can use its action to polymorph into a Medium humanoid, or back into its true form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Harmony. If more than one beatle is singing at a time, the DC of the Wisdom saving throw to resist being charmed increases. If three or more beatles are singing, the saving throw is DC 15. If two beatles are singing, the saving throw is DC 12.

Multiattack. The beatle makes two attacks: one with its claws and one with its club.

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.

Luring Song. The beatle sings a magical melody. Every humanoid and giant within 300 feet of the beatle that can hear the song must succeed on a DC 9 Wisdom saving throw or be charmed until the song ends. The beatle must take a bonus action on its subsequent turns to continue singing. It can stop singing at any time. The song ends if the beatle is incapacitated.

While charmed by the beatle, a target is incapacitated. If the charmed target is more than 5 feet away from the beatle, the target must move on its turn toward the beatle 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 beatle, 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 beatle's song for the next 24 hours.