Well, I may be new here, but I think I can contibute to this:
You may use most copyrighted assets in videos, webcomics or stuff of that sort so long you don´t basically make the same thing and attemp to get profit from it (bootlegs, rip-offs and so on).
But if what ou want to do is something like Original Characters, memes and the like, you may feel free to do that as long you do´t attempt to earn money (ad-enhanced links count in this)
In short, most companies allow their assets to be used so long it isn´t something too big, good or noticeable, so I wouldn´t recommend that path unless you´re going to make Sonic romhacks.
If you want to make a game about the player interacting with crossovered characters, well, while a good idea, as it would be likely impossible to also make it canon, that turns almost the whole point of it useless (as some players would like to make weird or innapropiate stuff with them, and a small few what you would have hoped for).
So I would recommend to just first make your own characters (witn no sort of player as avatar), then places that make your world different from the rest (this is why I like far more franchises that don´t just take real life-content and paste them into it with no noticeable changes other than the characters in there).
For example, I´ve noticed that the most iconic videogames have pretty special iconic places that put them apart from other series.
I would say more, but I think this should be more than enought.
In case you want more tips, I would also recommend this YouTube channel, it´s great for this purpose about developing videogames in a social sence.
If you still want to put copyrighted assets in the game however you can also just put an easter egg in the background, edited enought and not directly referenced toyou don´t get in trouble.
For example, putting a Starman from Mario into the shape of a candy that some kid is eating around (smaller, of a different color and with different texture propierties), which name he says is called "Stormy" or something like that.
Basically just keeping it subtle enought so only those smart enought can get it.
You may use most copyrighted assets in videos, webcomics or stuff of that sort so long you don´t basically make the same thing and attemp to get profit from it (bootlegs, rip-offs and so on).
But if what ou want to do is something like Original Characters, memes and the like, you may feel free to do that as long you do´t attempt to earn money (ad-enhanced links count in this)
In short, most companies allow their assets to be used so long it isn´t something too big, good or noticeable, so I wouldn´t recommend that path unless you´re going to make Sonic romhacks.
If you want to make a game about the player interacting with crossovered characters, well, while a good idea, as it would be likely impossible to also make it canon, that turns almost the whole point of it useless (as some players would like to make weird or innapropiate stuff with them, and a small few what you would have hoped for).
So I would recommend to just first make your own characters (witn no sort of player as avatar), then places that make your world different from the rest (this is why I like far more franchises that don´t just take real life-content and paste them into it with no noticeable changes other than the characters in there).
For example, I´ve noticed that the most iconic videogames have pretty special iconic places that put them apart from other series.
I would say more, but I think this should be more than enought.
In case you want more tips, I would also recommend this YouTube channel, it´s great for this purpose about developing videogames in a social sence.
If you still want to put copyrighted assets in the game however you can also just put an easter egg in the background, edited enought and not directly referenced toyou don´t get in trouble.
For example, putting a Starman from Mario into the shape of a candy that some kid is eating around (smaller, of a different color and with different texture propierties), which name he says is called "Stormy" or something like that.
Basically just keeping it subtle enought so only those smart enought can get it.