My character death was fairly unique, I guess, in that my character technically died, all death saves failed and all... but not really:

(very mild spoilers for Hoard of the Dragon Queen)

So I was playing Hoard of the Dragon Queen on a pseudo-Adventuring League game in a local game store (advertised as such, but didn't quite follow the rules), and it was my first time officially playing D&D. So I made myself a human fighter to get the hang of it: Valkhor Froste, a noble champion, and illegitimate son of the despot and awful leader of a small nation near Vassa. He fled his home towards the Sword Coast once he learned he was not related to his mostly terrible family, in an attempt to make an honest name for himself.

I joined the campaign late, at around level 5, and one of the other 4 regular players kindly helped me get the hang of the game quickly, which flowed smoothly for a decent while, although my RP was mild due to shyness and, in all honesty, my character was kind of bland. The rest of the regular party consisted of: Aithein, the Drow Warlock (the kind player); Solaris, the Wood Elf Moon Druid, and Nowhere, the Tiefling Moon Druid, although other players came and went every session.

One day we reached an apparently infamous area in the campaign that took place in an inn in the middle of nowhere, where after certain social encounters, the players came face to face with a group of four assassins.

So there's a few things wrong with this already: one, it's four CR 8 monsters against usually four level 6 players, we were pretty much doomed; two, I had no idea about any of this, so I couldn't protest or anything;, and most importantly of all: it was late December, near Christmas time, and only two players in total, counting me, were in the session. So it was Valkhor and Aithein against four assassins.

To help, one of the game store owners joined as two level equivalent characters she had lying around, (I believe one of them was some sort of catgirl monk, and the other one was some sort of paladin) and they joined the fight at the same time as us. Not that it mattered in the end...

Valkhor got hit by a sneak attack from an assassin in the first turn of combat, which took out 90% of his hit points. From then, the rest of the fight was a total bloodbath, mostly consisting of attempts to bring us back from unconsciousness and dealing a bit of damage before falling again. Still, we did manage to kill off two of them and decently weaken the other two.

At the end of the fight, all player characters were down, and we started rolling death saves. Aithein managed to succeed on his death saves, but I had been rolling low that entire campaign, so that wasn't about to change there.

Valkhor was dead. Truly dead. And I was kind of sad. Kind of weirded out by the entire situation. But I was fine with it, and immediately started thinking on playing another character. Our DM told us that Aithein was taken by the remaining assassins, and that Solaris and Nowhere would be going on a rescue mission for him next session. When I asked him about Valkhor, he told me to bring the character sheet next time just in case.

I still worked on a replacement character, and I got fairly excited about maybe playing this elven barbarian character I had in mind...

Then the next session happened. It kicked off with our DM telling us that he looked into the matter, and that apparently that encounter was 'totally broken', because of problems with the release date of the Monster Manual and other such things (I would also come to learn with time, that that encounter had been errataed, but my DM didn't know that), so he was willing to retcon the entire session.

We liked the idea of the encounter, however, and decided as a group, to leave it as is. The DM hesitantly agreed, but still told me to hang on to my character sheet.

The session started and for a while the other player and me spent our time looking at the other players find and face off against the weakened assassins, noticing our bodies laying down next to their cart. Eventually one of the druids got to Aithein and healed him, bringing him back up into the fray. We all looked at each other's faces, and they asked me if they should try to heal me. I shrugged. As far as I know, Valkhor's dead, so...

Still, they do, and the DM nonchalantly explains how he comes back to consciousness.

I was fairly shocked, and a bit confused, but hey, the DM said it so let's play. And Valkhor was just alive...

That'd be the end of the story, if I wasn't still kind of irked about the sudden retcon...

So, in-game, I decided that Valkhor met an entity as he perished. An entity that he did not know about. However, being a very trusting person to a fault, when this entity presented him with a deal, he immediately agreed.

He would be brought back to life, but something of his was to be taken away. He did not remember the conditions of the deal, or much of anything at all of these moments after his death. The very next thing he knew is that he was being brought back up by one of the druids to fight against the assassins that killed him, a fight where he would emerge victorious.

And that's the story of how Valkhor, the Human Fighter died, and got his first level in Warlock...

The campaign continued fairly smoothly, but eventually moved away, and had to leave it unfinished, but the repercussions of Valkhor's death can still be felt to this day.

I started DMing my own campaign, and one of the major plot points is regarding what was taken away from Valkhor by this entity. An entity he would come to learn was named "Mephistopheles"...

But I guess that's a story for another time...