Board Thread:Help desk/@comment-15305799-20160507200638/@comment-33173-20160507210955

AFAIK it's a mod done with cheat codes to make the game harder.

Unless you mean the Wave Command Cards to face giant viruses and golden DX bosses. The codes can be seen here. (Note that it's Japan and America only, it was removed in European version)

And Le Mu XA and RogueSX in the very end of the game, available after obtaining all Battle Cards. (excluding Star Cards)