Got it in one. Fire's a strong suit of his, wind's one of mine, so I could fan his flames and concentrate them on our target.

[ It sounds tidy, but they were in tunnels, so it was a smoky endeavor. ]

Took a couple rounds, but we turned it to ash. At the time, he thought it was a "mimic", which is apparently some predatory creature. It was taking the guise of supplies... Now whatever it is, it's topside. I agree with you that it's a problem.