I was thinking of a category where you have to complete adventure 1 and adventure 2 in a row.
It's very stupid, I know
That isn't a stuped idea, actually, it already exists a category for that in the Category Extensions leaderboard. https://www.speedrun.com/pvzce?h=Second_Adventure&x=wkpr1ow2
As AntBlueR said, it is a category extension for PC, Console and DS. There is no category extension page for Mobile as it is not a popular enough version of the game to justify adding a new leaderboard.