Mega Man Zero
The true Mega Man X was originally conceived as the antagonist of the Mega Man Zero series but was ultimately replaced with Copy X.
Mega Man Zero 2
A Rockman Zero/Mega Man Zero Collection was released for the Nintendo DS in June, 2010. It contained all four Zero games while making some slight modifications—mostly to text and dialogue. A gallery was added, as well as an Easy Scenario Mode, unlocking most upgrades from the start and allowing the player to progress through each entry in the quadrilogy consecutively.
Mega Man Zero 3
More so than any of the traditional Mega Man games, the Mega Man Zero series experimented with numerous new gameplay mechanics, weapon types, and methods for obtaining new techniques.
Mega Man Zero 4
In the Japanese version, characters would split in half when destroyed and spray red liquid. This effect was toned down considerably for the Western version.