Mega Man Xtreme, known as Rockman X: Cyber Mission (ロックマンX サイバーミッション) in Japan, is a video game developed by Capcom for the Game Boy Color handheld game console. It is a spin-off title in the Mega Man X series of video games and was followed by one direct sequel, Mega Man Xtreme 2. Chronologically, it takes place sometime between Mega Man X2 and Mega Man X3. The game is a downgraded port of Mega Man X for the SNES, featuring levels, bosses and other elements borrowed from that game, along with some levels from Mega Man X2 and some new content (for instance, a new storyline).
Mega Man Xtreme has three different difficulties: Normal, Hard, and Extreme. The difficulty determines what bosses the player faces.
Source: Wikipedia, Mega Man Xtreme , available under the CC-BY-SA License.