Just like in the first Paper Mario, there is an easter egg to revert Mario from paper to 8-bit sprite. Only this time it works on your partners too! In the X-Naut Base in Chapter Seven. Find the room with the swinging grate on Sublevel 2. Stand under it and use your Ultra Jump to jump up into the air vent. Press R and slide through the grate on the far right. You'll land in the changing room where Peach disguised herself, inside one of the stalls. When you pull back the curtain, you and your partner will be a sprite. This change does not affect game play and will wear off when you leave the room.