Mega Man ZX
Mega Man ZX
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Area N can be accessed from the Transerver room in Area M-3. In this area, while on Normal or Hard difficulty, you can obtain a Mysterious Rock after defeating either Spoiler:Omega (in his Zero form) from Mega Man Zero 3, or Spoiler:eight bosses with four each culled from Mega Man Zero 3 and Mega Man Zero 4. In order to access either set of four bosses in the latter method, you must be playing on an original DS or DS Lite, as the Game Boy Advance cartridges for either Zero 3 or Zero 4 must be inserted to gain access to them. In Mega Man Zero/ZX Legacy Collection, you can select either game to use for this bonus content via Link Mode before starting up Mega Man ZX.

After obtaining the Mysterious Rock, you can take it to Fleuve who will analyze and transform it into Spoiler:the Biometal Model O, allowing Vent or Aile to turn into Omega and use all of his attacks.
Contributed by MehDeletingLater
This was the first Mega Man game to feature a playable female protagonist (Aile).
Contributed by CosmykTheDolfyn
If you talk to a little girl "Sherry" in Area C-1 on your birthday, she will give you a piece of cake that heals 8 points of damage.
Contributed by gamemaster1991
The original Japanese version had voice acting for the entire game. The American version (with exceptions for the bosses and some cut scenes, which still have the Japanese voices) removed all of them to avoid confusion between translation dubs. This was fixed in the sequel, Mega Man ZX Advent.
Contributed by gamemaster1991