Rockman Cross X
Rockman Cross X is a hack for Rockman 5: Blues no Wana (not the overseas version, Mega Man 5) that changes the game into a boss-rush type with very little focus on platforming. All the bosses have been rewritten, giving each one new attacks not seen yet.
This hack is playable up to the second fortress stage, and features a good number of secret weapons and bosses. You may also enter a pure boss-rush where every boss is confronted in a random order by pressing Select on the title screen.