Aspel/Merri/Drake/Ari
When Fira hit the Elemental, it shuddered and floated backwards, which meant that yes, as Merri expected, fire could hurt the creature.
"Yes, Fire!" he called out to confirm Aspel's guess, following up with, "Maybe Thunder, too." Most water-based creatures were susceptible to lightning attacks as much as, if not more than, fire, so for good measure he decided to try Thundara. He had the time, now that Aspel yelled to keep and hold the Elementals' (where did the other one come from, he wondered in shock) attention, and he would not let her efforts go to waste. He only hoped that Barwater would hold.
Once ready, he tossed the spell towards the Elemental, but this time it only reared back without a shudder. Fire it was then. "Just Fire!" he amended, finally sheathing his sword. If physical attacks could not harm it, he was better off dualcasting until his mana became depleted or until the Elementals were defeated, whichever came first. If Faram smiled upon them, the Elementals would fall before Merri could not cast any longer.
But the Elemental's attention returned to Merri, and he, too, felt the familiar sensation of an attempt to be Silenced; fortunately, the bauble Owena had gifted him with before leaving Emillion rarely left his person, and he was unaffected. In the aftershock, however, he almost missed the sweet refrains of Ari's voice and song, and he already felt a lot better even as an Elemental tried to attack him with Watera again. His feet were better planted this time, so he only skidded back against the stone rather than take a tumble back on his back, and the pain was only momentary. When Aspel, too, took the blow of another water spell, Merri panicked that perhaps Barwater was not as effective as he'd hoped it would be, or that it hadn't worked at all, until he remembered Guy's tutelage: the spell would only lessen the blow but not fully protect against it. Still, Merri attempted one more time to cast it on Aspel for added measure.
He glanced behind him to try to find Ari, but the Mist was too thick and he couldn't look for too long. Instead, as Drake had Chi attacks, he decided to give Aspel one more boost of Enfire before he resumed his own spellcasting: two Fira spells, one for each Elemental, to be dealt at the same time once they were ready, and he hoped that his mana could hold out for as long as he continued this tactic.