I would suggest Mega Man Collection Powered Up. Basically Mega Man Powered up, but with 4 forms of graphics: 8-bit, 16-bit, and Mega Man 8 style. It includes Every Mega Man game up to the Sega Saturn version of Mega Man 8. It allows you to make your own stage, submit it by Wi-Fi Connection, and it costs only 800 DSi Points! In other words, mentioning the editor, it'll allow ANY boss in the series 1-8 to be placed in! It'll allow you to select modes known as:
Boss Rush
You place warps to specific bosses, like, for instance, all of the Fire-based Robot Masters. Yes it can be a mixed up variety of bosses. When testing/playing these, you get the abilities of every boss you will fight when you enter the stage.
Mini-boss Rush
Same as above, but with Mini-bosses. No special abilities but the Mega-Ball. You could be fighting the Ultra-Mini Boss only available to fight by beating all 8 games, or gathering the 8 Z Crystals (Mega Man X reference, but not the crystals) that are hidden, 1 per Mega Man Game.
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This mode is only unlockable by beating Bass' Story on Mega Man 6 Powered up.
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This mode is unlockable by being purchased in Mega Man 7 Powered up for 999 screws.
And more to come!