Seeing the swords be disrupted, and the smoke clearing to allow him to see how close the spellsword was, the younger cultist decided to simply let all his power loose.
Fire blasted from his form, sending both the elder Cultist and Marv flying, once again.
(You know, next time, you may want to ensure a healing person accompanies you.)
“She'd become a governess. It was one of the few jobs a known lady could do. And she'd taken to it well. She'd sworn that if she did indeed ever find herself dancing on rooftops with chimney sweeps she'd beat herself to death with her own umbrella.”
― Hogfather