The Mario Mash-Up Resource Pack under the Add-Ons section (in other words, the Mario Mash-Up texture pack) doesn't show the right textures in existing worlds that were created with the default Minecraft textures initially activated. Instead, it continues to show the default Minecraft textures with the default Minecraft music when the Mario Mash-Up Resource Pack is activated in a world and put at the top of the list of active resource packs. In addition, when looking in the Resource Packs tab in the Storage tab of the Settings page, the Mario Mash-Up Resource Pack doesn't appear with the other Resource Packs, but it appears in a world's settings page in the Resource Packs page under the Add-Ons section. However, the Mario Mash-Up Resource Pack works correctly in worlds that are created with the Mario Mash-Up Resource Pack initially activated, including the Mario Mash-Up Template World.