Under the domes (where GR wouldn't work) I prefer undead (like the one that comes from Army of Dead, but it doesn't really matter where it comes from) in the conditions of polar night. Bring enough undead and cast darkness+grip of winter+rain (probably it should be snow
) That makes one longdead roughly equal to one devil (less HP, but better att/def, and longdead are not getting tired), and it's not difficult to bring a mass of undead.