Hidden Bosses can be used once they have been defeated. The conditions of the Bosses to appear are to fulfill two out of the following three conditions. If you play with a Capcom groove you will get Ultimate Rugal, and if you play with a SNK groove you will get Shin Akuma.
The Custom Groove option appears once a normal Boss has been defeated (normal Akuma or Rugal). Normal Bosses appear by fulfilling two of the four following conditions:
The middle Boss appears when the following conditions are all fulfilled:
At the Groove selection screen, press Start.
Boss challenge mode becomes available under the following two conditions. Both hidden Bosses (Ultimate Rugal, Shin Akuma) must already be defeated and unlocked. Hold X + Y and press Start while highlighting arcade mode.
Highlighter any fighter at the character selection screen and press a button. Allow time to run out and the game will start in one on three tag team mode. Note: Do not select one on one battle mode.
Clear Boss challenge mode with no continues to unlock the "Extra Option".
While editing the colors for your character, press Start to display more options on the left side of the screen.
Defeat all characters straight in survival mode. The custom groove option settings will become infinite.
Hold Start + FP after winning a stage to make your character say an opponent specific quote. Hold Start + FK to make the character talk with a team member.
Beat up your opponent until his/her life is low enough to finish them off with a special KO. Stand near your opponent and wait for them to taunt you. Then, do the special move and you will get a finest KO. You also have to either beat the mini-Boss, or receive 1500 GPS before you finish the final round in Osaka to get to Ultimate Rugal.
Choose a good fighter such as Ken or Ryu. When you are facing the last Boss, if you are losing by one round and there is not a lot of power remaining, press Start on controller two and repeat until you win.
After unlocking the Extra Options, go to "Option Mode" at the main menu. Go to "Extra Options", select "Player One Life Gauge Type" and change it to "No Damage". Then, go to "Groove Gauge Type" and change it to "Infinite". After this, start survival mode and defeat all 46 characters without taking damage and your Groove Bar will always be full.