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Marius - demons - pointless
Nimus - poison - pointless
Aiden - intelligence - unnecessary
Khalid - sulfur + teaching the main hero is unnecessary
Zidar - magic - unnecessary
Ksarfax - chain lightning is just ridiculous
In general, they're all terrible!
Are "Spawn of Evil" skills pointless? I don't think so. Additional defense and attack never hurt.
Intelligence is unnecessary? Aiden can become an excellent mage with a huge amount of mana!