A few basic assumptions stayed unstated, and worked anyway. Things like "Each player takes a turn".
What did work was having five basic rules stay in play, and be there to be explicitly overwritten (fluxx style, though this was never stated either)
One formal rule we had was that after the game 'ended' the remaining players would each get a turn. (Preventing an 'I win' card, since we had no rule for playing outside of your turn, and no-one introduced one.) In future games, this will be a starting card.
We also decided (later on) that cards could be modified only whilst in hand, and you weren't allowed to cross stuff out, only add stuff.
The limited room on a card helped bring the game to a close.
Of especial interest was the self regulation of power - people tended to play cards of similar power and effect on the game. This seemed to be due to everyone else hanging onto a few blank cards, for writing into "Oh no you don't".
Formalising an "Everyone else says no" rule might be sensible.
And now, onto the important stuff: The silly cards.
The initial rules:
How do I... Start my turn?
Draw one card.
How do I... Play?
Play one card, on any (or no) player(s).
If you can't play a card from hand, instead draw two cards.
How do I... Stop?
The game ends when you can't play.
How do I... Win?
The player with the most points wins. (This card got replaced. A lot.)
Note that these initial rules (plus the unstated that the discard pile refills the draw pile when the draw pile empties) mean the game doesn't end easily. That wasn't a problem, since people changed the rules quite a lot. But you probably need to point this out before all the blanks are filled.
The fun stuff:
(I created some sample cards to get things started, then shuffled them in)
The player with the most animals wins.
(Not all that notable in itself, but it lead to such wonders as "One million lemmings.")
Draw the discard pile. One use. (The pile was about 70% of the deck at that point, then someone made everyone swap hands...)
Kibbits (the muppet)
Play cards from other players hands, instead of your own.
(And some memorable cards got created during play)
A card explodes. (One use)
The termite zoo is closed
This negates the effects of all vampire cards.
''(Of which there were two - 'basket of vampire kitten' and 'vampire smiley')
All points multipled by e to the iπ.
To each according to their rabbits.
Collect all cards in play, shuffle them, redistribute them randomly.
... With a little picture of a squirrel with a stop sign and everything.
Bury a card in the pile. Shuffle the pile. Pick out another card.
Scroll of city bus
Hit another card with a bus. (Stays on that card.)
This looks a prime category for play-by-wiki or by Serge's miraculous online game framework. If we can work out a good way to play it online, anyone up for a game over Easter? --Pallando
It really needs the pictures and the silliness of trying to draw pictures under a moderate time pressure to work well. (Being forced to play a: "The winning player is on" card due to the effects of a "You have five seconds to take your turn" was fun.) --Vitenka
Without the pictures and time-pressure it's essentially just Dvorak. -- Senji.