Doing a stealth run in old school WOW. They apparently felt we shouldn't do this, as they eventually added mobs in dungeons who could see through stealth to prevent it.
But before that, and I doubt I was the first to do this, but I know I came up with the idea on my own, I grabbed some random rogues and a pair of druids, and decided to try and farm boss mobs in dungeons that dropped good leather gear. Usual setup, 3 rogues, 1 tanky druid, and one healy druid. They'd be in cat form and hang back, and we'd sap/distract/lead away and vanish mobs to allow the others to sneak past. We'd be able to take shortcuts because we had someone with good lockpick, and basically do assassination runs on specific bosses to our hearts content. Got really good at it too. It was fun as hell, and was the first time where I felt being a sneaky bastard had tangible benefits in the game, that were also thematically appropriate. Sure, we couldn't take out the entire dungeon, and not every boss, so we'd miss out on other loot drops. But we could bypass defenses and get the one boss we wanted dead in like 10 minutes, and out without having to dedicate our entire night to some dungeon run.
Sadly, they patched that out after a while, and we couldn't do it anymore. But it was fun while it lasted!