Replaces the difficulty skulls with Ashley or Leyley from The Coffin of Andy and Leyley. There are 9 variations (Ashley: 7 and Leyley: 2), see images to find which one you like.
If you are interested in changing the texture yourself, you can check out my guide below. From the TOC, scroll down the to the "Menu/Interface Guides" section and then to "Difficulty Skulls".