Nerrisa or Faith's head
Since we are really baffled as to who was Nerissa, (was it Nerissa or was it Faith glamoured as Nerissa?), let's go baaaaaaaaaaaaack to episode 1. There were things that didn't seem quite right and questions which weren't really answered...
*Q 1: Okay, so some say that Faith really is alive and that the head we found in ep, 1 was Nerissa's. BUT, that head had the exact same bruise as to when Faith had when she encountered Woody. If that was her head, shouldn't she really be dead? But if that was Nerissa glamoured as Faith, where did she get that bruise? Was that just a make up or whatever?
So you say it was Nerissa glamoured as Faith, if that was Nerissa glamoured as Faith when she encountered Woody and the head we found was Faith's (the real Faith), where did she get that bruise then and where was Faith really?
It's really confusing. But we can't turn our heads away from this because it was this night, the night they found Faith/Nerissa's head, where Faith/Nerissa said lines that were exactly the same as the lines she said which were: "Do you like my ribbon?", "You're not as bad as everyone says you are" "I have to tell you something"
And the way she smokes in ep 1 is exactly the same as the way she smokes in ep. 5.
*Q 2: Okay so um..in ep 5 (btw I'm with theory #1 where it states that Faith was really alive and etc.) Faith said that she was the person who carefully placed Nerissa's head (glamoured as Faith) on the doorstep.
But let's look at the clues we found in ep. 1
First there was this track of blood and a blood on one of the sharp thingies found at the back where there was a garbage and all. So, does that tell us that Faith climbed there, got caught up on the gate which caused her to bleed and ripped a piece of her jeans because of that?
This thing wasn't really answered in the game, was it?
Please comment down on whatever idea you have and I'll reply on it! Let's help each other to solve this soooo soooo intriguing mystery!
Don't be so harsh. 
This is my first time putting my ideas here.
Comments
I always believed that Faith has been dead since before the beginning of the game, and Nerissa is the one we meet at the beginning. I figure you can take the evidence and look at it one way or another, so there is no definite confirmed answer as of right now.
Yea, whoever it was (Faith or Nerissa) got caught on the fence while leaving the Woodlands and putting the head there.
Yeah, thanks for the comment XD Perhaps you could read my other post too? http://www.telltalegames.com/community/discussion/91863/lily-s-death?new=1