Necromancer Spell: Cursed Earth
Here's an idea, a Necromancer or a group of necromancers can curse an area, and any people who die in that area, become powerful undead similar to the level of the person that died there.
Groups of Necromancers could bring about a turn in the battle where the fighting is heaviest and cause a high risk high reward threat to a zone being fought over by allies and enemies.
The thing is...this could just be NPCs...or it could be a 2nd life on the field where the dead aren't able to be brought back to life, but instead players linger on in this dead state until killed or their slowly draining HP pool empties. Enemies could be automatically turned into an NPC undead, but allies would have a limited new set of undead abilities they could use, and continue to interact with objectives that require people on the point to capture them, or interact with objects...too risky for the living to attempt to use.
Working backwards from this concept we can configure a strong group spell for the summoner class in general that might be workable in different ways for each different inflection of summoner.
Perhaps each dead player in this zone confers the ability to summon specific levels of a monster, whom one of the recently dead souls in the zone can possess if they're an ally.
I would love for this to also perhaps be something that the other inflections would get to have a flavor of.