Played chess the other day with my nephew (10). We hadn't played
   it in a year or two. First we played a regular game. Then it was
   his rules. It got VERY VERY complicated. Started off standard
   but by the time the game got going, the pieces had individual
   memory, intelligence, there was a complete trading system,
   one-use shields, additional special moves... It was interesting.
   Completely consistent within its own Universe, just like chess
   but with many more possibilities available than a chess game I
   just waited as new rules came up from him and I absorbed them
   and incorporated them. Strategy was beyond the 2D world of
   chess..