Gently Murderous Winter?

[MaxWilson]

Vs. Niefelheim? I doubt Beckoning would be cost-effective, given their high MR. Leprosy would help, but take forever to kill them. Flames From The Sky doesn't kill them but can sometimes give afflictions (you'd probably need 2 or 3 to actually kill more than 10% or so of the units).

Niefelheim is basically not vulnerable to artillery spells. You could try assassination spells instead, or battlefield enchantments like Plague (Woundflame) and Astral Tempest (on teleporting SCs if necessary).

-Max