"Why, Rick?"
#1- Rick makes a device to ensure success in the stock market. While it seems innocent enough at first, since the running gag of the time detective indicates it works by telling the future, it actually rivals his microverse battery for casual cruelty. It works by merging their reality with one where the stock they invested in were successful. The result is bone-chilling - whatever they invested in succeeds, and the rest of that alternate timeline is completely obliterated.
#2
- The Clackspire Labyrinth. It's a gigantic maze filled with the worst monsters, death traps, and other assorted hazards the galaxy has to offer. Criminals are sentenced to life in this place, which usually amounts to anywhere from a few seconds to months. Worst of all, it was created by Rick. One of the most deranged and unstable individuals alive, given absolute control over a section of land to warp into the deadliest place imaginable.
#3
- The class-2 clonerbeasts. Unlike the parasites of Total Rickall, these don't insert false memories to justify their presence. They just replace your loved ones, imitating them for weeks at a time until they have the opportunity to replace you too. And unlike the Rickall parasites, they'll fight back, playing mental games with the victims and displaying open sadism.
- We finally see the typical alternate dimension, the one where the characters are reversed. Here, Rick's the idiot and Morty's the genius. But unlike the main universe, the dynamic doesn't work. Fed up with his condescending attitude, Rick brains Morty with a hammer. No cosmic horror or alien monster here, just an ordinary man pushed too far.
- And that is just the tip of the nightmare fueled iceberg. If normal Rick can resort to this then there is a good chance that Morty could be pushed to this kind of breaking point. As would later be shown in Season 7, that's exactly what happened with Evil Morty, even if the hammer wasn't involved.
#7
- The interdimensional assassin beast. It's a pile of goo and spikes with a creepy melted face that hunts and kills every alternate version of its target. In its first appearance it murders a Rick and goes after his Morty, only failing because he escaped with the dead Rick's portal device. Even that doesn't work for long because it tracks him to the new dimension and kills him. Rick's immediate reaction to it was to run screaming about how they're all going to die. According to him it was responsible for the deaths of untold Ricks, enough that the increased death rate was noted by the Council of Ricks. And with all their knowledge and power, they still couldn't stop it.
#8
- The alternate Santa Claus, Mr. Chimney. He's disturbingly unhuman, can flay people to the bone with his voice, and doesn't bother acting like his spying isn't creepy, but that's not the half of it. He's omniscient to a horrifying degree, able to peer through dimensional barriers in addition to the standard 'watching you at all times'. Even Rick is scared of him.
#9
- In response to Morty's traumatized fear from all the brushes with death he's had, Rick gives him a box. If he opens the box he will experience death, giving him the knowledge of what lies beyond the mortal coil. We never get to know if he was telling the truth because Morty chooses blissful ignorance, but Rick implies that the answer is the reason he drinks.
#24
- In a parody of Event Horizon, Rick, Morty, and Summer stumble across a missing spaceship of Rick's design that had traveled to a hell dimension. While trying to use the ship's computer, Rick is locked on the bridge and the lights go out. They come back on (pictured) and boom, the room is flooded with blood and Rick is confronted by the ghostly visages of characters from the show (Xenon Bloom, Bird-Person, Nebulon, etc.) who he murdered or allowed to die, all asking, "Why, Rick?"
