Hadouken on X was a real "secret", but Shoryuken on X2 and Golden Armor on X3 had pretty much the same requirements (with X3 the player should not have any previous chip). It should have been nice if Capcom added the Tatsumaki Senpuu Kyaku (spinning helicopter kick, not a translation, I think) to X3, or X4 since it had no major secret, besides the code for Ultimate Armor. In X5 you still were able to find it ingame, but I haven't seen any secret like that on X6.Spoiler warning:
