Something I'm still not fully understanding

How exactly is it determined which difficulties you get to play for the Final/Extra stages in Supernova 2 and X?
What I remember:
B (combo broken) and lower: Nothing
B with a full combo:
A: and

I believe it's determined by which difficulty(or difficulties) you get an A (or full combo, I guess) on before Final Stage. I think beating a Challenge (or maybe a Challenge only song) can get a final stage song, but I don't remember what difficulty it gave.

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The difficulty is determined by the highest rating you got an A/AA on. So if you make a B on Expert but an A on Difficult, your final stage boss songs will be on Difficult. Or you could just enter in the unlock codes and then it doesn't matter 8)

the CS versions are set up so if you AA on heavy you have every difficulty available for the final stage, and the difficulty you AA that on determines what difficulty your ES/EES will be on (except for X2 when you unlock DEGRS and are forced onto oni). i dont know if the arcade versions behave this way or not.

if you dont AA, daiz nailed it. the highest difficulty you got an A on determines final stage difficulty.

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If you get an A on any of the normal stage songs, you unlock Extra Stage on all the difficulties that you got an A on. If you get an AA on any of the normal stage songs, you unlock Extra Stage on every difficulty. IIRC Challenge is never unlocked for Extra Stage songs, so any unlock that would have been on Challenge is instead moved to Expert.

Example:
1st Stage: A on
2nd Stage: B on
Final Stage: A on
Extra Stage gets unlocked for and . It would have been and but Challenge is always moved back to Expert.

If that Final Stage score had been an AA, you would have unlocked Extra Stage on all four difficulties, sans Challenge.

Wait a second I don't think anyone is getting this completely right. I just played a boat load of DDR X Arcade and here is what I observed for at least arcade versions, if you earn a A rating or higher on a specified difficulty on the stage before the final stage, you are offered a default song to play for your final stage at that difficulty. If you pick a different song or different difficulty then the chance for extra stage is void. However you must get a AA rating on the default song at the specified default difficulty for the final stage to unlock extra stage. In Extra stage I believe you can pick whatever song but you are locked into whatever difficulty you played your final stage. Playing anything than the presented default song will again end the game after the round. In extra stage these days you are presented with a oni-point meter to survive on, the number of hit points you get is based on your performance of the Final Stage, a score of 950,000 or higher will only award 1, a score of 970,000 or higher will give 2, a score of 980,000 or higher will give 3, and a score of 990,000 or higher will give a full 4 hit points. Simply passing the extra stage at the default song choice will unlock Encore Extra Stage, where that is played with only 1 oni hit point at a specified song (a.k.a. sudden death). In final stage and extra stage you can choose whatever options you want to make it easier or harder (to your preference), and I believe that to be true for most encore extra stages except for DDR X2 arcade. I believe console versions follow the rules I have presented just as much except difficultly choosen for the second to the final stage is not mandated to what difficulty is selected in final stage.

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You're almost there; the life bar's a little more lenient on X than it is on Supernova 2, and so the minimum number of lives you have for Extra Stage is 2 at 950,000, with 1 more each at 962,000 and 975,000. Also you can play Random on Final stage to get ES, but not for EES (this is all in regards to DDR X, SN2 lets you get EES from ES random) but your final stage difficulty has to be the same as a song you AAed or Aed earlier. (And for some reason challenge doesn't count)

Well at least I got most of it right considering I play on something newer than SuperNOVA about every 4 months.

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