Inferno’s main forces.

Demons don't work very well with neutral creatures. Because if you use demonesses (if you choose them instead of succubi), you can end up hurting your own troops. There will be morale problems... And they won't be able to open gates...

Why take joined neutral creatures into battle? They should be used for experience as soon as possible. The main strength of demons lies in the demons themselves, not in the joined neutral creatures – they are just a source of extra experience.