Unlock Maniac Mode
Beat the game on Expert Mode to unlock Maniac mode.
Unlock New Mini-Games
Boss Survival - Finish the game with both characters
Rockman [Mega Man] a (Antique) - Finish the game on Beginner or Expert Mode
Secret Model
Collect all 24 medals from bosses. Start a new game and play until you got Model A, then go to use item "a" in your inventory. Credit goes to PuiKung.