The Sign of the Great Old Elder God From Beyond (2010)

From the Game's Introduction:
This is a game for two players. One player will take the role of the mad worshipper, bent on manifesting the Great Old Elder God From Beyond here on Earth, and the other will act as the avatar of the Great Old Elder God From Beyond itself. (You may play the game multiple times, alternating roles, at your own risk.)

User Summary:
The avatar secretly decides a physical action that the worshipper must perform in order to summon the eldritch horror of unfathomable doom. The worshipper then asks yes/no questions in order to determine what must be done.
With each successful query by the worshipper, the avatar chooses one of the words they just used. The worshipper can no longer pronounce that word, able only to utter gibberish in its place.
Play continues, optionally using tokens to track progress and force an end-game, with the worshipper attempting to discern and then perform the required somatic component to the summoning spell.