What I mean is, if you look at the Warcraft III Cenematic where Hellscream fights Mannoroth, Mannoroth is big but not as big as a mountain. In outland if you go to the Pools of Aggonar that Pit Lord is the size of a freaking mountain! So why are alot of races like this? Why is Mannoroth so small compared to other Pit Lords?

Not all demons are the same size.