For my niece's 7th birthday she wanted a Wipeout birthday... She loves the show and specifically asked for the cake to have the three big red balls in blue, not muddy, water with happy birthday avah written on the balls... No small order. She also wanted the cake to be half chocolate and half vanilla but I couldn't figure out how to do that without making it marble so I made the base chocolate and the water and the balls were vanilla. The bridge was graham crackers dipped in blue colored white chocolate.
Here are some pics of the cake coming together..
Used a special pan to make the 1/2 ball shapes and then just icing them and put them together to make the big red balls for the cake...
My messy work space and the covering of the graham crackers: