Necromancers – “Assault” [Campaign 3, Mission 2]

He also leveled up Attack, which is a debatable choice, and whether it's even needed. But there are no mentors here, so it is what it is, without Summoning.

Then level up the Cold Steel perk to somehow justify this skill. You'll deal ice damage in melee combat against the undead; it's easy to level up, you just need basic attack skills.