This is an idea from the last I decided worked good enough on its own.
You were going about your day when you found somehow in small canyon where you found a strange colorful building that looks like a motel but theirs no office just a just structure with with some rooms and doors to them along with a floating neon sign that reads media motel and also a floating note that reads do what you like traveler. Every room has a poster of fictional franchise over its doors and the room itself is themed around that franchise if you say the name of a character of a character from that franchise the room based around it then that character will appear in the room with they will not try to harm no matter who the character is though they will still have their personality intact you can summon multiple characters from the same room and multiple of the same character the rooms cant be destroyed or have strange properties removed. . If they leave the canyon reality will change so that they’re home and belongings exist also the suggestibility wears off and they can harm you. theirs also a stack of notes beside the door each room each note has a character from the franchise the room is themed after and if you into the room holding a note physically become the character whos name is written on it and gain access to their voice skills memories mannerisms clothing and powers also some strange force urges you take the note at top of the stack or say a character name in the room. The franchises the rooms give you access to are basically infinite or there’s one for every franchise currently in existence but the one you know about are all near the entrance
(Side note it doesn’t work if you try transform or summon into any godlike beings or reality bender can’t be anything with world ending power also the characters cant harm you or the world in any way while inside the canyon and rooms aren't affected by being bigger than them being inside them)
Theirs also giant futuristic looking that seems to be infinite upon entrance and has keypad that if type something into will suddenly transport you to a store that that(but wont just normal not anything like the solution world problems or cosmic power in a box) also anything in the mall is free and is their is no staff in said mall once you transform into a character you will have a sudden urge to got to this mall which has a giant sign floating over it that reads interest mall
If you go into a room while as a character from the franchise the room is based off and say undone you will separated from the character being returned to your original body and said character will exist in the room with you and their personality skillset and identity will be a mix of their original and what you did as them in the interest mall example( alma madrigal in a console/game store she will be a gamer when you separate or toriel in a video store you separate she will be a youtuber and also when you summon a character they will be somewhat suggestive if you tell them to go to the mall one of the rooms or leave the canyon they will do it but not much else if a character goes into a room holding a picture of a different character they will become a fusion of those character same thing if you go in as a character transformed (example: dash parr+ Mirabel madrigal = either a slightly order Mirabel who has speed gift or a Columbian female superhero who’s a friend of violet or her cousin if you separate from the fusion
(Side note also know nothing about the rooms and mall your just going off the some glowing writing on the ceiling that says: behold the media motel ever wanted the ultimate cosplay ever wanted to hangout with your favorite character ever wanted to make your fan fiction come true well now you take a note from pile by the door specifically the one with the name of the character you want to cosplay as and then enter the room don’t if you want to remove said cosplay all you have to do is undone in said room if you want to just hangout with your favorite character then just go into the room without a note and say their name and don’t forget to go see the interest mall and make your fantasies come true)
Also if you leave the canyon as a character you can’t separate once you enter again
So which franchise do you got to do you transform or summon who do summon/transform into how do you react what do you do in the interest mall and how does this change the character