The day my players stole the macguffin in a oneshot
So I'm a relatively new DM. I've been a player for 2 years, and I just finished Lost Mine of Phandelver. I replaced the BBEG with my own, and added a magic artifact that they found.
Well I decided it would be fun to have the players run a oneshot as a group of goblins hired to steal a lockbox from a mansion. They didn't know common, so they couldn't interrogate guards, and I never hinted that it was in universe.
It was organised like this: there would be a pre-heist prep phase where they could spend 400gp on equiptment, Intel, or services. Intel consisted of blueprints, and security info, services were distractions, or bribing a guard to leave a door unlocked. Equipment was anything from the PHB, as well as darkness, and silence bombs which were heavily depowered versions of the spells. Several guards would patrol the building in real time, and the players would have to dodge them.
The players bought blueprints, 2 silence bombs, a darkness bomb, and info about patrol routes, and a minor distraction in the form of a group of bards coming to the front door.
They made a plan to enter through the back service entrance. They made their way to the back, but then the thief rolled poorly, and couldn't pick the difficult lock, which set off an alarm spell. Abandoning that plan, they decided to run to the window closest to the target room right as guards came around the corner. Then they threw a silence bombs at the window, smashed it open, murdered the sleeping inhabitants of the room after climbing through the window. The arcane trickster illusioned the window to look fixed, and kept it up everytime the guards came close. They easily made their way to the target room, and then all almost died trying to solve the magic puzzle which was securing the box to the desk, before sneaking back out the window, and off to safety.
The best part, however, was the look on their faces when the goblin chief opened the box, and pulled out the artifact they just found. Then it donned on one of the players that they had stolen his 400gp, and his diamond for casting chromatic orb.
Now they're dead set on finding those damn goblins and killing every single one of them.