It was a killer dungeon game at Origins this year. We were supposed to go into the dungeon to stop some major evil thing from destroying the world (though we ended up actually freeing it, which was bad).
We’d entered the dungeon and found a wizard’s lab/chambers. There were a bunch of interesting things around the room. Being a one-shot, most of them were bad/dangerous. I think someone found an intelligent ring that did
vampiric touch, but it would drain you if you didn’t keep it topped off. Anyway, there was a cloth over a dome. The cleric went over, pulled the cloth off, and the DM does likewise at the table, revealing a skeletal hand in the jar. The cleric opens it, the DM gives him a saving throw, and he rolls a 1.
What followed after that is the cleric immediately put his hand on the table and chopped it off with his axe, and then he held the
hand of Vecna to the stump. At that point, he gradually started turning into Vecna. The DM told us later that he had never had that actually happen, so he was scrambling to try to prevent the game from getting completely derailed. As the cleric’s powering up, we’re trying to take him down before he kills us. No one died, but I’m pretty sure at least one person went down. In the end, we managed to knock the cleric out and chop the hand back off before it was permanent. I’m pretty sure that’s not how things are supposed to work, but (again) the DM didn’t want to derail the game (as awesome as that would have been).
We ended up completing the dungeon, encountering some nasty traps but overcoming them. He was using Grimtooth’s for his traps, which was also great. In the end, we couldn’t overcome the big nasty at the end. Well, we won, but we also lost. It was a killer dungeon, so that’s expected, and it’s probably best it happened at the very end when was also revealed we were tricked into coming here to unleash the big nasty.
Overall, it was the most fun I’ve had playing 5e, but my sample size for that is extremely small. I’d totally do it again next year if they’re running something again.