How can I implement a 2D character in a 3D environment

Okay, so I'm playing around with Unity 5.1 and I'm trying to create a 2D/3D blend of a game. Basically I want a 2D character in a 3D world, kind of like the mechanics in Fez to give an example. I've created a sprite sheet and cut all the animations I need into an animation controller. I've created a quad that has a rigidbody and box collider for my character, which also uses a sprite renderer to display the animations. And that seems to work except when I play the game I get this 'trail' behind my character (I've included a picture). I assume this is because I'm trying to mix a sprite renderer and 3D physics, so is there a fix to this or is my whole approach wrong?

I'm pretty new so there might be an easy solution but I haven't found anything yet. Thanks for any help!