[Endoperez]

Something that might work even better than Flames From The Sky is Fires From Afar. It is available long before Domes, especially if your friend is not ready for it. It might only target 10+ units/commanders, but if you mass Fever Fetishes you will, in theory at least, be able to kill off quite a few of his mages. Surprising your friend seems to be important, and you must take everything you can from it. To cast many Fires From Afar you need Fetishes, and for them you need Nature gems. Conquer as many forests as you can, and scan them with Haruspex as soon as possible.

Considering Artifacts. If you forge Alchemist's Stone (5F+5E, in gems), and it is Wished away, your friend just used 90! gems and a turn of his high-buffed pretender stealing something your non-buffed nationals can easily forge... He might do it though, as alchemizing gems from massed Fetishes should work really well!

I would like to know why you are playing with the same pretender. For me, it seems that it is good for his strategy and not so good for yours. You might do better with stronger scales instead of high astral, as your are not trying to do the same as him.

I don't have experience in anything like your duel, so heed my "advice" with care...