Zarron gets his face filleted by fiery flames as the floating face flings a fierce fireball. He miraculously turns his body at the last minute, but still gets frightfully fried. (19 damage, assuming half damage on a save).

All tactical thoughts forgotten at his brush with fiery death, the young bard immediately, almost reflexively, casts his most damaging spell, designed to center around the skull and avoid hitting anybody else around him.

"Age, tonitru. Concute inimicos meos!"

Move behind cover.
Cast Shatter vs skull (don't hit Ghiso or Taara)
Skull must succeed on DC 14 CON save to halve (3d8)[16] thunder damage. A creature made of inorganic material such as stone, crystal, or metal has disadvantage on this saving throw.