The upside of having used Dissolution on it is that the damage is continuous just as the fire had been, meaning that the construct is going to be slowly falling apart while they hack at it.

While both the burning and dissolving are active, he can manifest other abilities, but at a greater cost to his personal energy reserves. He'd have to wait until the next shift in the thing's weak points to be able to reactivate either one and so for the time being, the best he can do is strike out at the rib where he was directed, circling back around while it lunges and launching a ranged Snap that would chip off part of the bone and further cripple it. The next one would be more effective at least as he was able to light a new fire.

"Camilla?" he calls to check in on her. If she takes that hit, her defenses would no longer be fortified. He needs to know that she can fend for herself until he can re-up it.