I realise it's 100% predictable of me to be enamoured with metatextual wankery, but I really appreciate the textual conceit in Nobilis whereby the game is ostensibly an in-universe document (i.e., the tabletop RPG Nobilis exists in the setting of Nobilis), particularly in light of the 3rd Edition's revelation that author's fictionalised self-insert is a human thrall of the generic Excrucian Deceiver who keeps popping up in the game's examples of play, with its concomitant implication that the game's systems of play are in-universe Excrucian propaganda. Like, forget about unreliable narrators – this one has unreliable rules!
Game idea: Don't Call Cthulhu. You are all cultists, but none of you REALLY want to summon the Great Old Ones to destroy and recreate the world in their own fearsome image; however, you dare not appear reluctant, lest you get used as a sacrifice by more fanatical cultists.
Game mechanics revolve around coming up with reasonable-sounding objections to starting the ritual now, arguing against those objections so you don't look like you're giving in easily, and finding ways to uphold any objections while still making it seem like progress has been made towards starting the ritual.
Eg, "we don't have any chalk to draw the diagram", "we can just get some chalk", "we need the highest-quality chalk possible in order to do this perfectly, which we'll need to special order".