scary sphere question

ok so this is my first time posting on the forums, i don't know much about c# in fact i am a novice at best when coding so as for my question i am working on a third person game where you run around in a cartoony environment. when you get close to an enemy a small sphere around the player and the enemy turns into a hellish environment. what i have done, i have made the map for the normal mode and i have made the hellish map how do i go about making the landscape change to the hellish mode? here are some pictures of what i mean and it is also a 3d game thank you if you can help or have any ideas

 

You could achieve this effect with 2 cameras using different layer masks.
Put normal world on one set of layers, and hell on another.
Make the hell camera render after the normal (so it draws ontop) then do something clever to control the shape of the hell rendering.

 

Easier said than done though :/

 

thats a really cool idea, how do you think i would go about it like have the sphere of the hell world as a round section on a camera?

 

Heres a video with a round camera view, youll have to do some smart maths to get the round part moving to track the target