Althought nonw of the paper mario sagas have happened yet, they will probably go straight in a row in order, without specials in between, this may change though.
All the paper mario sagas take place in alternate dimension. Luigi accedentily gets pulled into Proffesor E.Gadd's dimension traveling machine, or, EDTM (E.Gadd Dimension travel machine), or the Egadddimensionandspaceynesstravelingmachinethingy, as E.Gadd calls it. Mario goes after Luigi and makes friends with his alter demension self, paper mario. Luigi isn't found until the point in super paper mario where, in the game, they meet up with Luigi In the underwear. Luigi From Mario's dimension does NOT turn into Mr. L, but his alternate form (who's first seen as Mr. L) is Mr. L, and is forever evil. When Mario and Luigi return, Mr. L sneaks with them, and temporaraly works for bowser.