Go to the first Secret Dungeon - Desert and go all the way back to the room with an 
item chest and a Forbidden Device. To the north of this room, you can get off your 
E.S. Continue along the path. With the Sequencer D, you can dive into another secret 
location, the Space Coliseum. In here, talk with Black Hakase/Professor to trigger an 
event and eventually you will end up fighting Black Erde Kasier.