The chances for stepping randomly when you move in the tundra is 1/3, and 1/10 in the desert. (1/4, 1/14 if you have the luck skill.)
Currently Fire Masters can step confidently in the tundra, but get blown about in the desert. The desert, however, contains twisters, which may throw the unlucky FM onto water, killing him instantly.
Now personally, I kind of like this, however I'm being persistently informed that it makes FMs too weak. I like it because it offers much more strategy; Can you kind a desert crossing point that's twister free? Maybe you could convince some friendly WMs to build temples on all the twisters in your path? Dare you risk it?
On the other hand, there could still be danger when crossing from the border of the tundra into the desert.
Anyway, so the option's there, or if you want to suggest another change regarding FMs, do so.
What if FM could somehow destroy or relocate twisters? Maybe fireball at the twister could do one of four things (probabilities could be weighted): a/y - twister is destroyed (the twister is consumed in flame) b/y - twister is pushed back (hot air currents force the twister back) c/y - no effect (the twister consumes the fireball) d/y - twister grows (the hot air accelerates the twister, causing it to spread to an adjacent square)
FM's still conquer the frozen lands (being masters of fire, and all), and if the twisters bother them so much, they could spend fireballs trying to get through the desert.
Not sure if the moving or growing might instead become a weapon.
Twisters always throw you 1 or 2 squares, anywhere in your normal visible radius.
I'm not going to do something that moves twisters; all "special" tiles on the GoG map are based on a set algorithm of moduluses which keeps them fairly evenly spaced. Spam, you're ignoring the Occam's Razor principle for likelihood-of-idea-implementation. (The simplest get in.)