Lots of games have unused content in them. Run 3 is no exception, of course.
The Climber
The Climber is an unused character in Run 3, which is referenced in the pictures. She is simply called "Climber" and she looks like the Runner. Player 03 has confirmed her existence on the Discord, claiming she was an idea he once had, but isn't sure she'll make it in the game. However, she may be planned for Run 4, as Player 03 said she was not slated to appear in "this" game.
Multiple Wormholes
The Achievement "A Glimpse of New Places" used to say "Locate the first wormhole" with a lowercase w, suggesting that more than one wormhole was initially planned. Even Player 03 forgot why he changed it though.