DP x Under the Whispering Door crossover where Danny periodically visits Charon's Crossing anytime he is especially close to becoming a full ghost.
I'm debating on whether or not he remembers after each visit, but I think it'd be fun, and a little weird, for Mei, Hugo, and Wallace to go ??? every time he shows up.
The first time, everything's normal with how they greet ghosts and they give him some tea- the works you know? Even Wallace is helping out. Nelson thinks it's funny that there's another ghost who figures out their powers quicker than Wallace and teases him about it. Nelson is also very appreciative that Danny can take and dish out jokes so well. Apollo is just a very happy for a new person to smell and play with.
The next time they're all a little confused, but hey whatever, maybe this time it'll be for real. They enjoy their time with Danny again and Danny even mentions a different ghost dog friend of his, which gets Apollo's tag wagging and very excited.
By the third time- which would be post-canon for UTWD- Wallace is very much "hey, you need to be more careful and stop doing stupid shit while you're alive"
Each visit after that boils down to "??? why is he still coming back what the heck. Also, he doesn't remember us, but he always knows how to use ghost powers instantly??? WHY?!" <- it is mostly Wallace saying this, the others just enjoy their time with Danny. Although, Hugo is also confused, but he is much more polite about it.
Danny doesn't really get the problem, but he has a lot of fun in this weird tea shop and appreciates all the free food they give him (Wallace is soooo pissed in the background like "why does HE get to eat stuff as a ghost?! fucking ripoff" but like, more in a Wallace way of saying things). Though, he always wakes up with the distinct feeling of someone- or someones- yelling at him to be more careful. Danny never really thinks much of it though, assuming it was just Sam and Tucker yelling at him while he was unconscious.