Mega Man Battle Network 2 Cheats for Gameboy Advance
To be able to unlock Hard mode you have to get the 5 Stars.
Unlock Yellow Star:
Complete Story Mode by beating Gospel in Apartment Tower
Unlock Red Star:
Collect 250 Chips in your Library Database
Unlock Blue Star:
Complete 31 Program Advances
Unlock Green Star:
Beat the original Planet Man, Pharoah Man, Napalm Man and the real Bass in the WWW area
Unlock Purple Star:
Collect the other 10 secret Chips in your Library Database - Chips 251-260
When you have collected the 5 Stars highlight 'New Game' and press Left, Left, Right, Left, Right, Left, Right, Right, then select new game and save 'Hard Mode'.