Goemon "History" Lesson
Before turning on the Power, insert Konami's recently released "Kessakusen! Ganbare Goemon 1+2" (Gameboy Advance) into the DS, along with the new "Ganbare Goemon: Toukai Douchuu Daiedo Tenguri" (DS). Now, at select locations throughout the game, various characters from the GBA game will appear! Speak to them for some interesting dialogue or perhaps even more...?!
Note: that these NPCs will *ONLY* appear while you have the GBA Goemon 1+2 cartridge in the DS!
Alternate costumes:
Collect all 30 Elephant Statues to unlock new costumes for all four characters.
Mystical Ninja History Lessons:
Also have the Game Boy Advance game Kessakusen! Ganbare Goemon 1+2 inserted. At select locations throughout the game, various characters from the Game Boy Advance game will appear and tell you things about Goemon's past.
Space-Manbo mini-game:
Also have the Game Boy Advance game Kessakusen! Ganbare Goemon 1+2 inserted. At the mini game menu, Space-Manbo will now be unlocked.
Goemon New Age Shutsudou! reference:
In the second town's underground prison, New Aged Goemon can be found occupying the second jail cell for his "crimes against the Goemon franchise".