Multiattack

The swarm of fire dancers can use its Frightening Visage, if available. It then makes two Singe attacks.

Singe

Melee Weapon Attack: +8 to hit, reach 0 ft., one target in the swarm's space. Hit: 22 (4d10) fire damage, or 11 (2d10) fire damage if the swarm has half its hp or fewer.

Frightening Visage (Recharge 5-6)

The swarm rearranges itself into the shape of a giant, blue, flaming Humanoid skull. Each Humanoid within 30 feet of the swarm that can see it must succeed on a DC 16 Wisdom saving throw or be frightened for 1 minute. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.