Beat the game under normal difficulty to unlock hard mode. Also, if you finish the game at normal or higher with Vent and Aile, starting a new game from that clear data will allow you to keep Model X after getting Model ZX.
Mega Man Zero 3 and 4 bosses:
Have the Mega Man Zero 3 or Mega Man Zero 4 GBA cartridges in your DS while playing to see bosses from those two games in ZX.
This sounds trickier than it is. After clearing Area M, make sure to send your mission report and save and all that jazz. Go to the other side of Transerver to Area N, and proceed to the second floor. Use model HX to get past the metal floors and spikes, and you'll be at a door. Inside you'll fight Omega Zero, the final boss from MMZ3. After winning, go back to where you started to get to Area N and proceed to the top floor. You'll see two doors that require MMZ3 or 4 GBA cartidges to open, and past them a third door. Behind that third door is a floating rock, Grab it and leave. Then show the rock to Flueve. He'll analyze it and give you Biometal OX.
Beat up the doll in Prarie's room, and it will eventually drop a W-Can, which refills all your biometal energy. You can only carry one at a time, but the doll will always drop it when you need one.
Set the system date to your birth date (also in system). Then head to area C-1 and talk to Sherry. She's in one of the rooms with a dark door. She'll give you Birthday Cake, which restores 8 bars of health
Boss dolls: Get a level 4 victory over a boss by not hitting their Bio-metal parts. If you're succesful you'll unlock a doll of the boss that sits in Prarie's room.
|Fistleo||Avoid his head|
|Flammole||Avoid his arms|
|Hivolt||Avoid his wings|
|Hurricaune||Avoid her neck|
|Leganchor||Avoid his head|
|Lurerre||Avoid her head|
|Protectos||Avoid his chest|
|Purprill||Avoid his arms|
Thanks to Revolution Readers cut-dude, Fish Man, and Craft!