From 2017 to 2021, I was involved in a more-or-less-weekly D&D 5e campaign. It was the best pick-up group I’ve ever had – the GM put out a solicitation for players on the Roll20.net forums and all of us tagged in. One guy dropped after a half-dozen sessions but the rest stayed with it for the whole time, from 1st level all the way to 17th.

PC death was always on the table, but I somehow managed to have one of two original PCs who survived to the end of the campaign (and the other sacrificed himself in the final session to pull off a world-saving magical deed). This was because I was running Tiashash, a dragonborn barbarian/fighter who, by the end of the campaign, and with the help of “top half of the hit die” and “reroll level-up hit die with inspiration” house rules, was approaching 250 hit points.

One of the other long-running PCs – the other original-party survivor, in fact – was Rimble, a gnome wizard. We pretty quickly figured out that our DM also house-ruled that damage resistance would stack – half-damage from one effect and half-damage from a second effect equaled quarter-damage. This enabled some interesting tactics, like Tiashash raging, running hell-bent-for-leather into a group of enemies, getting their attention, and then standing there while Rimble dropped a max-level fireball on him. Invariably, between the rage and advantage on Reflex saves, Tiashash would be standing there, slightly smoking, at the center of a pile of smoldering corpses.

I think it took until 14th or 15th level for Tiashash to actually go down to zero hit points from anything, and that was the DM basically saying “enough of this shit” and hammering him with psychic damage.