What is your favorite ultimate ability for that class?

Regarding the scenario where the enemy attacks first...
It's unlikely they'll do so if they have a large army. However, if it happens, the mage could lose most of their army...
BUT... if they win, they'll gain a huge amount of experience and possibly a Skill Point.

The enemy will also have a large army. Therefore, they will do it if they can reach the mage. Moreover, unlike the mage with an underdeveloped Skill Point, they will have some magic or battle cries. Therefore, the mage will most likely lose their entire army.

However, against an Orc with Sympathy and Counterspell, another mage's Skill Point will be useless. It simply won't allow them to cast spells. In a long game, they should have enough mana for almost the entire battle. However, in my Zehir's case with such a build, the mana ran out during a battle with Biara. But by that time, Biara had almost nothing left of her army.