This forum game will probably fail, because I'm good at that. Please tell me if there is already an existing active forum game like this.
A ball of... most items known or reasonably imaginable to mankind floats in the universe, only barely bigger than the largest star, VY Canis Majoris (which is 1,420 time bigger than the Sun).
The objective of this game is to make the ball as small as possible. Destruction will start out slow, being able to take off or destroy pieces as large as a human at first. Use your imaginations, though. The possibilities are endless!
Most items you will be able to use against the ball can be found directly on or inside it, with rarer or more hazardous materials being found deeper.
If an action or item is too destructive or generally too large to be done at the ball's current state, then an action or item similar but smaller will be preformed or used, if possible.
Of course, you can also create things on the ball that can later destroy it, but will also count towards it's current size.
More rules might be added during the game's progression if I see that it's necessary.