I need to know if its possible to make interactive shadows?

Okay so first I need you guys to know I have barely began to learn how to use Unity, I have spent most of my recent time learning to use blender. So that means that I don't have the ability to test any advice you give yet. I am merely checking to see if one of the main features of the game I have plained it possible, if not then I have to rethink the whole thing. However if you think of a way to make you work give me some detials on it anyway so I can count how many ways there are for me to go about making it work, Second as said before I am using Blender to make all characters objects and enviroments. So make sure your suggestion will work with what I make with that program.

Okay so in may game Shadows play a huge part in it's mechanics. First they act as gateways from one to another. So the characters will be able to move through one and come out another. I wanted to achieve this by having it so if a character is standing on the shadow of a tree they came enter it. Second Characters can manipulate their own shadows increasing thier size and shape. Some of them can move them along the ground and when they touch another character they can grab them with the shadow. Some characters can also collide their shadow with anothers to do damage or control their body. So Shadow collisions with characters and other shadows are important. I'm kind of thinking I'm going to have to make the shadow an object in it's self but unsure how I can make it act like that of a character like mimicing and following them till it's otherwise active.

So does anyone have any ideas on how to do this?