Mega Man Battle Network 4 Blue Moon Cheats

There is a large hole surrounded by purple slime on a platform in Ura Internet area 6. In order to approach it, you need the chips ''Bug Curse'', ''Muramasa Blade'', ''Black Wing'', ''Element Dark'' and ''Poison Anubis''. Once you get close enough, it will suck you down to the secret dungeon, Black Earth.

One more thing to add:

To fight Duo SP, you need to have all the 7 symbols

1 for Duo
1 for Soul Complete
1 for Standard library complete
1 for Mega Library Complete
1 for Giga Library Complete
1 for P.A. Complete
1 for Forte SP

Go back to where Duo was and fight him there!

After defeating Forte in Ura Internet 5, Forte SP can be randomly encountered in Black Earth 2. He can drop Delta Ray Edge in Blue Moon, and Black Barrier in Red Sun.

To get past the gate in Ura Internet area 5, you need all 150 regular chips. Once you get past it, you can fight the secret boss, Forte, and get his chip, Forte Another.