It was just last month, after 4 or so years of playing TTRPGs (alright, D&D).
We were doing a chain of one shots. One player would DM an one shot, then the next would continue from one of the hooks left by the last DM.
In my case, the party was lvl 11 when I got the DM seat, and I was so nervous that I over prepared so much that there was enough material for 3 or 4 sessions.
I ended up using my own writings as a guideline and improvising most of the game.

The story was pretty basic. In the previous session we defeated this witch that was the subordinate of some Collector guy that was the head of the local blackmarket.
We found out that it was a mindflayer and that's where I had to pick up from.
I made the black market in question a fleshy demi-plane with all manners of patrons. From the usual drow elf to talking giant spiders, to an Aboleth that dealt in the buying and selling of memories. Everything was crafted to either be a future plot hook or something that would be relevant when they tried to fuck with the black market or when they finally came face to face with the Collector.
It ended with them going into a portal that led them to what was essentially a trap, with things like a mind controlled young green dragon that wanted to eat the gobling warlock, two zombie beholders with all but one eye stalk removed (one with paralysis the other with disintegrate), a death kiss, and the Collector himself at the end of the long hallway like area laughing his eccentric ass off while using his macguffin to control de dragon, make the room sprout tentacles to hold the party in place, send psychic blasts, etc.
They managed to get through that through both brain and brawl, and even stopped the Collector from teleporting away by using an artifact that they stole from the black market auction earlier.

It was actually pretty fun.