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Supric, since you say that Inferno is your favorite faction, I want to share some thoughts. Perhaps you've already considered them...
A/ The Necromancer upgrade shouldn't be removed. On the contrary, it's a good opportunity for Inferno to have a strong start. We need to fight the opponent using their own tactics against them.
B/ What can be used to counter the "immobile ghosts + 1 skeleton" battle tactic? Are you not building broodmothers? Maybe you should. They drain mana from the enemy and give it to you, then they become ranged attackers, and maybe they also deal magic damage? (I'm not sure). And the ghosts won't be able to retaliate against ranged attacks.
C/ Regeneration can be removed with dispel magic (which is available from level 1, right?). And even better, apply Regeneration to your broodmothers at the same time.
D/ You can leave the skeleton alone; let it live. If you use C and D, the enemy might have some serious mana problems.
E/ Apply Blizzard to the ghosts (it's available at level 5).
F/ And there are many other things you can come up with.
Or was the final battle more complex than the "ghosts + 1 skeleton" scheme? Please describe the final battle in more detail. I'm very interested...