The Single Player mode of MM8BDM is essentially a play through all the maps in the game with set bots. After so many levels, the player fights special bosses exclusive to singleplayer.
The story of the game takes place one year after the events of Mega Man 6.
After Mega Man defeated Dr. Wily for the 6th time, the real Mr. X was found and rescued. In celebration of his heroic efforts, Mr. X hosted the second annual robot master tournament with new rules and arenas. With permission from Dr. Light, each robot would have to be reprogrammed use the weapon swapping abilities of Mega Man to keep the competition fair.
During the final announcement of the tournament, Mega Man and Dr. Light's television is interrupted by Dr. Wily. He states that the tournament is a great idea, and that he wishes to prove his genius by entering all his robots to prove once and for all that Dr. Wily is superior to Dr. Light. There are no leads on where Dr. Wily could be hiding, or what he could be plotting.
Recently, a unknown robot (named Maestro by default, although the name can be changed) has taken residence in the Light household, planning on joining the tournament.
Dr. Light decides to enter Mega Man, his other creations, and this newcomer into the tournament to ensure Dr. Wily doesn't have anything hidden up his sleeves...
The player starts in Dr. Light's lab where Dr. Light explains the situation and briefly how to configure their controls. The player character is a unique robot to the series, a robot known as Maestro, created by an unknown person for the purpose of watching over the events of the Tournament (by entering it), and putting a stop anything that intervenes with the event.
The game is split up into chapters. Each chapter features Robot Master stages from their respective Mega Man games.
|Chapter 1:||Mega Man||Mega Man?||None|
|Chapter 2:||Mega Man 2||Guts Dozer||Enker|
|Chapter 3:||Mega Man 3||Mega Man?(Round 2)||None|
|Chapter 4:||Mega Man 4||Met Catcher & Metool Daddy||Punk|
|Chapter 5:||Mega Man 5||Mega Man?(Round 3)||None|
|Chapter 6:||Mega Man 6||Reprogrammed Robot Masters||Ballade|
|Chapter 7:||Mega Man 7||Bass||Wily Capsule|
|Chapter 8:||Mega Man 8||Duo||None|
|Chapter 9:||Mega Man & Bass||King||None|
|Chapter 10:||Wily Tower||Buster Rod G.||None|
|Chapter 11:||Mega Man 9||Proto Man|
Boss Rush Mode
Prior to v3a, upon beating the game, a new mode is unlocked called Boss Rush mode. In this mode the player simply fought nearly all the bosses in the game without having to go through each chapter, save for Enker, Punk, Ballade and Wily Capsule. After beating all the bosses, the game's ending plays as if you beat Chapter 6. Boss Rush can be found in Auto's section of the lab.
This feature was removed in v3a, presumably because of the redesigned save feature allowing the player to jump to any point reached in the campaign, including bosses. The functionality is still in the game, however — by typing "set secret_bossrush 1" into the console before entering a boss level, the game will automatically move on to the next boss. As of v4a, all bosses after Chapter 6 are accounted for, including Duo, Buster Rod G, Mega Water S, and Hyper Storm H.
The feature returns in V5, renamed to Boss Attack. After Plug Man returns to Light Labs, and all chapters are beaten, Plug Man allows you to attempt Boss Attack. In this mode the player is given three tries to beat the following bosses back to back: