The Undefeated Deluxe Pack contains:
*
* 7 Wallpapers 1600x900
* All Character and Important NPC Artworks
* 2 bonus Savefiles (Badass and God Modes)

How to find the deluxe contents

From your computer, go to:
C:\Program Files (x86)\Steam\steamapps\common
Then select the game folder.

Or directly from the Steam Client, first right-click on the game, then select:
Properties > Local Files > Browse Local Files

EXAMPLE