Recently, the modder known as Speclizer published a teaser for multiplayer in The Last of Us Part II Remastered, and has now presented a full development diary.
Problems arose at the very beginning: it was necessary to somehow represent a second player, but the game had no NPC that could move like a player character.
The closest option Speclizer could find was an NPC version of Ellie from one episode.. He extracted the model and began using it for the "second player."
Initially, the animations of NPC Ellie differed noticeably from those of the original heroine, but Speclizer found the necessary elements in the files responsible for movement and made adjustments.
For now, this multiplayer is just an "experiment," and Speclizer does not plan to release it, but everything may change during the course of development.