Maybe instead of hippos, we could make some trolls? Not the kind that live under bridges (like in Heroes 3 and 4), but more like in Warcraft or Gothic... They were huge there... seriously!))
Ogres also come in different sizes... but trolls are either very small (under-bridge trolls) or huge. Ogres are more of a medium size... and they can sometimes be mages.))
P.S. Although, we could keep the monster and just give it a different name... hmm... maybe Deathclaw?)) I know it's from Fallout...)))) or something similar.
P.S. Regarding the artwork... we could have Behemoths with tentacles. Although the ones from Heroes 3 would also work... Illusions are difficult to draw... and maybe an Ifrit, in armor. I'll describe it in more detail on ICQ.