All my 4chans post on the Happiest Apocalypse on Earth

Someone who’s not me wrote:

Sounds fun. During lockdown I ran a campaign where the classic Disney characters (with the serial numbers filed off; "Mickey" was "Ricardo Rat", "Donald Duck" was "Dolan, Aarakorca lich" "Walter Elias Disney" was "Dr. Elias Walter" etc.) were essentially ink golems who had tricked their wizard master out of possession of a magic book that let them re-write reality. The PC's had to enter the pseudo-realm the golems had created, steal back the book, and excise the cancerous demi plane before it could over-write all of existence. Also Eldritch-abomination Christopher Robin made an appearance. It was fun.

To your concern about your players though, I started the game without saying overtly "You guys are going to Disneyland!" I basically just had one of them get kidnapped by Aarakocra-Lich Dolan, and then slowly put more "Disney" characters into the mix until they figured it out (one of the early sessions had them enter a deserted village and fight plague Doctors named "Hugh, Doog, and Lugh" who were color-coded in red, blue, and green. Destroying their masks revealed them to be skeletal duck people).

TL;DR: If you're going for a twilight-zone vibe, just have them make up standard Apocalypse-world PCs (maybe steal some splat from this one to give them more options if you want to be generous) and tell them as little as possible about the actual nature of the park until they figure it out.