Antaeus's transformation was perfect, in my opinion: demonic, but not necessarily a demon, and humanoid, but not necessarily human. It's a clever juxtaposition of what the Frozen Flame can potentially do to a person's humanity. Turning into Kasmir would have been a little corny, and on top of that, it would be a mighty drastic change to the timeline, non? I'm not sure, but had Marle not interfered, wouldn't Antaeus have simply been killed?
Oh and Cedric Guardia rising to power through corrupt means is brilliant! It brings to mind how we tend to only revere or condemn historical figures on their actions, as opposed to the content of their character.