Waiting until after his allies unleashes their attacks and breaths, Levi swims upwards and forward to be in range where he can affect the crowd (35 ft from enemies) with his flock of piranhas if needed and shifts the darkness 10ft upwards so that his allies have a clear vision on the enemies. He summons the swarm in a space that will cover two enemies in his radius, prioritizing the hag and area that exclude his allies.

Spoiler: OOC
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Swift action elevate deeper darkness 10 ft upwards.

Summon piranhas swarm, targeting the half-fiend green hag and half-fiend merrow without including allies in radius if possible and in range. Otherwise, target two merrows.

Swarm Damage: (1d6)[6]

If damaged, inflict bleeding (Lose 1 HP per round). Fort DC 13 or nauseated.