Paper Mario Beta Archive (TTYD Spoilers)さんのイラストまとめ

Super Paper Mario contains unused sprites of every previous partner from PM64/TTYD, except for Sushie. However, all of these partners, including Sushie, can be found on Catch Cards in the final game.

A Whomp falls towards Mario in a fortress area. (9/10)

Mario bounces on a single Goomba multiple times using a move similar to Power Bounce or Hopslipper. (7/10)

Mario walks through a jungle area on a path surrounded by poison with a long Wiggler walking across. (2/10)

Paper Mario 64 also had unused Ninji palette swaps with five different colors. https://t.co/ikWNAXtqQC

There is an unused sprite of a scrapped enemy known as the "okooru" in Paper Mario TTYD. This enemy likely would've become angry if the meter on its head was in the red area since "okooru" means "to get angry".

The concept art of Paper Mario: Color Splash includes early designs for the Rock Paper Wizard including a Toad dressed like a Duplighost and a Lantern Ghost.

The Fortress from the E3 2010 trailer/screenshots heavily resembles Shhwonk Fortress from Chapter 1 of TTYD.

Sprites of an early Gooper Blooper design were found in the files of the final release of Sticker Star.