Has anyone ever run a game where the players are actual monsters? Like, a party of orcs, or drow or something? I know AD&D metiones this possibility in one of the core books, but I'm curious how often--if ever--people play this way?
Yep, I've done it a couple of times.
Most recently, the player characters fell through a portal into the Feywild and were transformed: for the duration of their stay there, they would have the form of a Fey creature. They would change back to their normal forms when (if?) they returned home, but in the meantime they would be monsters.
I let them choose any Fey creature they wanted with three stipulations: it had to be the same size as their current character, it had to be CR 3 or less, and nobody could choose the same one twice (the characters were all 6th level.) So the rogue chose Quickling, the druid chose Dryad, the warlock chose Green Hag, the fighter chose Satyr, and the paladin chose Darkling (Elder). They used the NPC stat block and character sheet in Roll20 for their "Fey-form" character, and away we went. It was interesting watching them learn how to use their new abilities and equipment to find their way home.
On another occasion, my niece (age 9 at the time) wanted to play D&D with us, and she wanted to play a unicorn. So I just copied the MM stats onto a standard character sheet, filled in the gaps as best I could, and ran with it. I think I posted about it already a while ago...yep,
here's the link.