Mega Man Xtreme is a Game Boy Color game containing slightly scaled-down stages, bosses and music from Mega Man X and Mega Man X2. Just like the Game Boy Mega Man games... but with a few tweaks.
GameShark code 0101A8D3 or Game Genie code A87-93B-7FF will enable a level select menu. Simply, load a stage with the code on, and it will take you to the Level Select menu.
The top two numbers represent the stage, and the bottom numbers represent "checkpoints". You can only use 00~05 when selecting checkpoints, and selecting 05 for a checkpoint takes you directly to the boss.
Loaded in Storm Eagle's stage, graphics of the broken window in the tower where the heart tank is found. They were probably only to be used when played on a Game Boy Color, in which case overlay graphics are used for the window and were to be replaced by these so the player could see inside. The final does not have the window break at all, so consequently, GBC players are not able to see through it while inside.
By enabling the Super Game Boy flag located at 0x0146 and modifying it to 03, or using Game Genie code 031-46F-E6A, you can enable a Super Game Boy single blue palette. Super Game Boy programming appears to have been in active development and was discontinued right around the planning stages for the border. This disables the Super Game Boy border screensavers.
Notice how the "Licensed by Nintendo" screen is glitched-out when Super Game Boy features are enabled and that both X and the game logo in the title screen appear with inverted colors.
This needs some investigation. Discuss ideas and findings on the talk page. Specifically: Has the flag activated automatically for anyone else on an Everdrive GB? (Edit by user who owns an X7)
The colors in the copyright info were also changed, due to it sharing the palette with the title logo. The "Press Start" was also changed, though this clearly doesn't seem intentional, as the lightest shade of grey is now an odd blue color that blends in with the background. The sequel uses the Japanese graphic in all regions.
For some reason, Vile is referred to as his Japanese name "VAVA" in the International versions. This error was not corrected in the Virtual Console re-release.
A portion of the stage select seen briefly in the cutscene after clearing the opening stage looks slightly different from the actual stage select, having unique detailing around the Sigma emblem area:
