I started playing a map on Veteran difficulty. I noticed the same mana issue with the Knight.
A small suggestion regarding Rupert's specialization: it should have the same chance to cast a single-target speed spell on each unit, rather than a general spell, to reduce the randomness. In this case, the chance of being left with nothing is lower, as is the chance of speeding up the entire army at once at the beginning of the battle.
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