Re: Demons
First of all, cast Magic Shackles level 3 straight away. The demons are highly dependent on their abilities, which make them very dangerous.
If you don't have one already, find a unit with high initiative that will enable you to have the first move.
For me demons were a breeze with Sprites, Lake Fairies, Elves, Hunters, Skeleton Archers. Also had Anga's Ruby.