How to beat 15 Pythium mages plus lions and wyverns

[Viajero]

Yup, I have around 4-5 turns more before I attack. From the spells mentioned I will only have acces to Flight but we have one of those global spells on that prevents flying anyways, Eternal Storms or something. Does that one prevent flying across map only or also in battle mode?

[K]

He's summoned crap units and he has a pile of mages.

Basically, the answer is "send in some chaff to catch spells, and when the morale breaks on his summoned crap you get an auto-win".

Don't fear this guy. The only mistake you can make is to let him get some research for spells that actually matter. On turn 33 his best tactic is probably Mind Burn spam; the problem is that he'll only get three turns of that before your archers cause his whole army to route.