The thing follows him and tries dizzying him again.

Sure, feel free to do that, but then Theo will shake himself out of it and he's moving quite quickly and then he pulls up and tries to get away.

Any convenient obstacles he can dodge around to get out the way?

There are mountains.

They are not really convenient obstacles to dodge around.

No. No they are not. Perhaps Theo should've learnt how to cast spells when he had the chance, earlier.

Yes. Perhaps he should have. Maybe he will, once he gets away from the thing, and in the meantime, alkali. (Slowly.)

The thing will continue attacking him and slowly melting.

Theo might try using some more dangerous chemicals – he's heard fluorine is disgusting and there are various compounds that make it worse – but he is not that desperate to get rid of it and also kill off the local wildlife so he currently opts not to.

Hopefully the local area can deal with alkali. Hopefully not too much is dropping on it. Okay, well, it's probably gonna end up killing the local area anyway, but at least it won't set it on fire, whatever.

There isn't much in the way of local wildlife, what with all the cold and snow. There are some evergreens.

Eventually the thing dies.

Well. He'd rather not blow up the snow, but alkali on the snow shouldn't be too bad.

Theo continues flying.

He will eventually (after a long, long time flying and maybe a few more flying fiends) find the cave's other entrance.

Then he can follow the road from above and not get attacked by any fiends on the ground. Hopefully.

He wishes flying were more fun.

Flying over the road must be significantly easier than walking it was, given the way it goes over and around and under itself in knots. There are bits of ruins covered in snow here and there, and eventually the road finds some thermal springs.

Oh, fun.

Anyone there?

...no one alive. The walls of the cave around the springs, however, are covered with statues, and a magical blue light flows over them and into the water. There's also a large sphere of water floating above the spring's surface, revolving slowly around itself.

Does the sphere look like it might have pyreflies in if he goes up close to it? Does it do anything if he pokes it?

It doesn't seem to have pyreflies in it, no, but then again, magic water usually doesn't. Poking it disturbs it much more than would be naively expected, but after shaking a lot for a bit it returns to its spherical status.

Weirdo water sphere.

What if he sticks his whole arm in it?

It tingles.

… What if he just decides to fly into the water, because yay experimental method.

It tingles some more!

...oh faces.

There are faces in the water?

Yep. Or in his head. One of those.

Well he's now gonna swim out of the water and see if the faces are still present.

They're not.