I've been playing Risk for over 15 years now, but never read the rules until just now.
Very interesting.
I've been playing some weird, strange made up rules in the past with my mates it would appear. (They had been playing it 10 years before I joined, and had come up with their way of playing the game, and I played to those rules for the 15 years)
Their rules were: Mission cards, escalating (cards go up in mutiples of 3, up to 30, then down to 3 and back up again) adjacent forts, maximum number of cards to be allowed to be held is 4 before handing them in (jokers included in the deck)
But what struck me in reading the rules was;
World domination - you play escalating cards.
and for
Mission cards - you play flat rate.
I didn't come across the no cards option anywhere.
