I noticed that going AM reduces your spellpower pretty much infinitely.
Seems like casting damaging spells with negative spellpower does negative damage.
Negative damage still kills things.
Using the Helm of Dwarven Emperors vide infra we have access to a spell as an Anti-Magic character.
Note the "inf light damage" in the description.

Using the active of this item results in dealing absurd amounts of negative damage.

Apparently -9x10^18 damage kills things.
To put this number into perspective, the distance from the earth to the sun in millimetres is only 1.52x10^14.
This hat is dealing Sixty Thousand times more damage that that.
Yes. It is fun.
I think I've found out how to make Doomed viable.