Here's a neat one most people probably don't know about, for the US version of
DanceDanceRevolution EXTREME for PS2:
There's a song in the arcade version of
DDR EXTREME called "Memories" that, under normal circumstances, is never unlocked in the US PS2 version. It's not a particularly noteworthy, difficult, or even good song, but people who looked into the game's data found that the data for "Memories" did indeed exist on the disc but the song could never be unlocked through normal play, and Konami stayed completely silent about it and never even recognized it as a thing. Most people just assumed that it was planned to be included, but was axed at the last second for whatever reason...
... until two years later, in 2006, when Konami totally randomly and without warning revealed a button-based code to unlock the song
as part of a fucking Burger King promotion. Keep in mind, one or two more North American
DDR games for PS2 had already come out by this point, and people had long since moved on from
EXTREME and the random mystery of Memories being in the game but not being able to be unlocked or accessed in any way.
It was so weird to pop the game back in, put in the code, see that it actually worked, and finally unlock that last elusive song... which, again, isn't even that good and certainly not much of a bonus for arcade players who had played the song a million and one times by then anyway. Kinda crazy that Konami put in a song that they knew they had no intention of ever letting people unlock for another two years!
Saving your game in MGS with a timestamp of 11:11:11...
I'll bite. What does this do?