The multiverse, a concept of multiple realities across a vast open space. Anything is possible with these universes, you can find anything, do anything, be anything, you can even meet yourself from a different reality and if you're lucky enough, there's cartoon characters. Moving on, just in between the multiverse, there's a playground, a place where if you imagine it, it can happen. You somehow enter this realm, you see a what seems to be infinitely large plain of land, with cartoon characters roaming around. And not just them, there's game, book, show, movie, anime and manga characters

You don't need a list if you know what characters you can think of are here. When arriving you see a guy floating up in front of you, he looks to be the creator of this place

Anonymous: "Yeah, hi. Welcome to the Multiverse Playground, where characters reside, anything you imagine will exist, blah blah blah... Anyways let's cut to the chase, no I'm not God, nor am I Jesus or any holy figure, whatever you think I look like, I'll have that feature. I just have power here and can send you in and out any time I want. I'll follow you around and watch your every move, don't sweat it dude I won't judge your actions. Also call me what you like, I don't care"

With that, in this place, you see the lands of different characters from different genres, like the Regular Show Park, Equestria from MLP, the land of Ooo from Adventure Time. The guy follows you when you go somewhere, he takes the form of an orb as it's the most common floating thing

Anonymous: "Have fun around here. Also no need to worry about being gone for long, time works weirdly here, when here time freezes in all universes. So if you're gone for 50 years, 0 seconds for your home"