It's like someone took all the TV shows and YouTubes I've been watching this weekend and put them in a blender.
I was in a version of the universe which had a grimy, tentacly parallel world like in Stranger Things. I was able to move freely between the worlds, even though most people couldn't perceive it.
My own ability to perceive it was apparently new, because where I had expected to see a bank of cubbies and a wall, suddenly the wall was gone and the bank of cubbies was twice as wide as it was before. There were the normal cubbies, and then mirrored across the plane where the wall used to be (so more of a lateral mirror universe than an Upside Down) was a collection of gross, dirty cubbies made of milk crates, like the one on the League.
I retrieved a package out one of the dirty cubbies, which had been left there for me by Chidi from The Good Place. This a safe and convenient way for us to pass things between the two worlds, because most people couldn't access them.
I took the package into the (normal, non-mirror) bathroom and opened it up, and out came a creature, part robot, part organic. Like it had the tank-style wheels of Johnny Five or Wall-E, but it's head area had just an insect's probiscus with a tiny, narrow tongue which came out and sniffed around for a bit and then quit moving, very obviously dead.
It died because it was made of antimatter, as all things in the mirror universe were, and it couldn't survive in a regular matter environment. Apparently there was no problem with handling antimatter in our world, you just couldn't have living things cuz they need antimatter air and food to live. It made me really sad to see it die.
There was more stuff where I was trying to track down a cassette tape on which was recorded some info that I needed, but there were a bunch of identical tapes and I had to try to play them in these 2 tape decks to narrow down my search. But the matter tapes would only play in the matter tape deck, and the antimatter tapes would only play in the antimatter tape deck, and I couldn't tell which was which except for trying to play them, but if I got it wrong it would destroy the tape.