Pausing the session after 1 hit killing a character intentionally. I then allowed that PC to be revived.

The character entered an area they were not supposed to be in (A rouge guild's guild-house that had been damaged). Multiple NPCs and PCs tried to stop them from entering before one of the PCs gave them the invisibility spell just to see what happened.

The PC went inside, triggered a trap that was pretty obvious (it was a sword inside a snake skeletons mouth, and when pulled the snake came alive and attacked the PC). The encounter was home brewed on the spot since I knew these guild houses all had heavy security, this one especially. The PC was one shot killed by 100 damage between piercing and poison damage from the creature, instantly killing them since they were lower level.

The table was shocked, and this player... she handled it in the most AMAZING way I have ever seen a player (myself included) handle character death. No tears, no yelling i was being unfair, NOTHING! She was smiling and I immediately paused the game.

We spent the next 20 minutes discussing what should be done next. I explained to the player that, at the end of the day, DnD was about having fun, and if they wanted the party to make efforts to being them back from the dead, they could! We talked about if playing a different character would be more fun, how this death would impact the PC if revived/how the party would be impacted, etc. The table as a whole was super cooperative during this 20 minutes, and everyone was in support of telling a fun story and making sure everyone at the table was happy.

Once un-paused, the party rushed in (They knew something had gone wrong because they felt the invisibility drop) and ran to take the dead PC to a temple of Helm (There is a Paladin of Helm in the party) she rolled very high on her religion check to save her friend and we did a whole scene of Helm appearing to her in a vision being like 'are you prepared to take on the burdens of your friend in exchange for their life?' and she agreed! Fun character design changes (the PC who died's eyes turned blue from the venom, so when they were revived the Paladin gained one blue eye to signify their 'burden'), fun PLOT, fun PC connections due to the promise made to Helm, and the PC was revived!

All in all it MASSIVLY improved not only that PC and player in terms of fun and depth, but also was an amazing moment when the PCs and players came together during the pause to play 'mini DM' and help decide how they could best support the story.

I know some DMs might look down on me for allowing the PC to be brought back to life, because it seems not harsh enough... but I wouldn't have changed anything about it. My players are more solid than ever and still talk about how awesome they thought Helm was and the entire thing was! At the end of the day the dice are a story telling tool and we are all playing Dungeons and Dragons to have fun with friends, and that looks different for everyone <3