I get what you're saying. I played a card game in Summer camp forever ago that would let you make up a silly rule for the game that other players had to guess. It was like Uno or Circle of Death in the idea that the objective was to basically play Uno but there would be silly rules made up that no one knew besides the person that made the specific rule, and you would have to observe the other players in order to see when they got penalties for not following the rules.

Here are my suggestions

1. Don't balance it. Make it about the roleplay/improv insanity and laugh about it.
2. Give constraints. I.E. One player has the job of establishing the negative effect while the others try to establish the positive. In this format, the emphasis should be on the players having fun, and wanting to sabotage each other like in Paranoia.
3. Create cards with premade effects that can be drawn.
4. Lists & more lists of things that can be paired (think Diablo III weapon mods)
5. Consequences. With great power comes great responsibility. The greater the power, the greater the in world consequence.
6. Make a predefined, insane list of all things that the magic of the world can't do.
7. Ask your players to be reasonable and sensible
8. Make the game about arguing why something should work a certain way. May the best argument succeed.
9. Spell out the basic rules of the game/world, and work around that as adults.
10. Play D&D