I agree with most of everything said. But just to add some clarity. The summon menu shows off which "main" pred you'll be pulling. In the top left corner when you are on the summoning screen. As indicated by the X5 beside their image. Everything else is kinda meant to just be feed for da Orca.
While certainly not every detail is given in the descriptions of enemies and allies alike. The demon lord does actually state most of the info. Using the mummy for example. The demon lord tells you that she is in fact an attack buffer. When fully fed of course. She also grants a cooldown reduction buff when fed undead enemies. (As seen by a golden glow/shading enveloping the mummy after eating a zombie.) So, while yes, some units have been given a more so "last minute" description. Rather than a fully developed log of info and flavor text. I personally haven't seen any that was unclear enough. That I couldn't grasp what they do.
This was just to help clarify. Not trying to attack or anything of that nature. <3