The rules Calvin and I use for playing ping pong now. It does remind me of Calvinball from Calvin and Hobbes.
It is played like regular ping pong but extra points can be added to the point being played for. One extra point is added to the current point being played every time a ball is hit over the wires that hold the lights. One extra point is also added if the ball hits one of the lights or the wire. One extra point is added if the ball bounces off the house or the window. Two extra points are added if the ball bounces off one of the stucco trim sections that makes a nice plonk noise if the ball hits it (I believe those trim pieces are foam covered in stucco). The points can keep getting added. So for example:
Calvin hits a serve. I return it and hit it over the lights. Calvin returns that hit. Then I hit it off the house. The point is now worth 3 points. 1 point for the regular point +1 for over the lights and +1 for off the house. Whoever wins this "point" will get 3 points. There is no limit to the number of points that can be scored.
You can also score an additional point if you win the rally from a let or if you win the rally from a ball hitting the edge of the table.
When we rally for serve you can also get extra points added on by hitting over the lights, off the house, etc. Then those points are applied to your score at the beginning of the game.
We recently added negative points. So if you hit a volley the current points being played for go down 1. So if you hit a serve and the returning player volleys the ball and it goes in and no one returns that then that point was worth nothing. If the current level of points for a play goes into negative because there are multiple volleys then you will want to lose that point. Because the winner of that point will get the negative points applied to their score.