Live and Learn!

Atem was allowed to return right after the Ceremonial Duel, he was given his own body, lots of fun puzzle/blindshipping shenanigans ensue, then Yugi and Atem DIE at the ripe old age of 100 and show up in the Duat. (Atem maaayyyyyy have made it a condition of his return to die at the same time as Yugi. shhhh. Yugi definitely doesn't have any complaints about that at all)

anyway, they get help from Mahaad making their way through the Duat. Atem is HOPING to avoid going to the Scales at all because he's worried about his penalty game stuff being counted against Yugi's heart since he was in Yugi's body when he did that. Spoiler: they do not manage to go around the Scales, they get plonked down and Thoth and Anubis scoop out Yugi's heart to weigh, Atem is NOT THRILLED at seeing this but it's fine, they get through it

then it's Atem's turn

and uhhh

things go a bit bonkers

When Atem no longer has his heart, he basically has no… conscience? sort of? that's a little extreme but it's the best I can come up with. So he reverts to sort of being the Spirit of the Puzzle, with his only instinct of Protect Yugi and Hide The Puzzle's Secrets (in this series' canon, he was aware inside the Puzzle for all the years and he was sorta endlessly tasked with "building" and mapping the labyrinth inside) so he gets all huge and shadowy and scary and starts building labyrinth walls and—

and Yugi steps in! literally! he steps into the big Shadow Atem and Atem absorbs him and Yugi lets him borrow his heart once more, so things don't get borked :) and the drawing here spins it a little bit, makes it so Shadow Atem holds him up, sheltering him, sheltering his guiding light, his HEART, oh it's so good

(this also means for a little bit, Atem gets to keep Yugi's spirit in HIS body, a reversal of their first dynamic!!!!)

Mahaad is able to conjure things, and they died in their pajamas, so Atem gets him to conjure them up some clothes in HIS style hehe, that's why Yugi is dressed like that

FUN RIGHT? <3

YOOOOOOOOO THAT IS VERY COOL!!!! THANK YOU FOR THE SUMMARY :D