The mechanics are very creative and tie directly into the theme. The Weather Reaction Table, which links the environment to specific mask expressions, is a brilliant and evocative idea. Forcing players to wear masks, like a crown of carrots or a potato with many eyes, or suffer damage is another great touch that reinforces the strange, surreal nature of the party.
The entire document is a great example of a concise and usable social horror scenario. Well done on a very creative submission!