For makjang type crazy. There is no one more absurd in making dramas like writer Im Sunghan. Dear Heaven is definitely hers. I think her current drama Durians Affair has crazy plot, same with some of my fave of hers Miss Mermaid, new Tales of a Gisaeng. Though probably none as crazy as Apgujeong Midnight Sun (this one i just read articles, didnt watch this) where she went and declared retirement after backlash of the on and off screen craziness.
For other unusual plots, maybe:
- Kotaro Lives alone - its not batshit crazy plot but as the title states, its kotaro living alone, but kotaro is just a kid living alone and meets the different residents of the apartment complex. Very interesting plot tbh for a very interesting drama
Fantasy/sci-fi/supernatural elements:
- Vampire Idol - vampire planet with vampire prince who has his very handsome vampire posey as they try to idols on earth after being stranded
- Go princess Go
- See you in my 19th life
- Marigold in 4 minutes