One of my biggest gripes with the "Mario" franchise is that you rarely get to play as Luigi ... or anyone aside from Mario. Granted, namesakes usually DO dominate the playing time (save for poor Zelda), but think how much fun several of the Mario games would have been with a second playthough as the Eternal Understudy, Luigi himself.
Well, from browsing cheats after I beat "Mario Galaxy" (yes, I waited until I had beaten it, not a moment before) I learned that capturing all 120 stars let you play the whole game as Luigi.
It's taken about a month or more to finish collecting the last 59 stars — thanks in no small part to this job thing and a trip to Dallas — but I'm two stars away (both in the Gusty Garden Galaxy) from completion. Then, I shall unleash carnage the likes of which Luigi fans have only dreamed of.