 The stage structure is different from other games in the series . After the introduction level , the player can only choose between three Robot Masters . <unk> Cold Man unlocks Burner Man and Pirate Man ; defeating Astro Man unlocks Dynamo Man , Tengu Man , and Pirate Man ; and defeating Ground Man unlocks Magic Man and Tengu Man . Clearing one of these unlocked stages opens the way to a security room where the player must destroy a series of crystals with obtained Robot Master weapons . <unk> all eight crystals opens the way to the fortress stages . In a similar fashion to previous installments in the series , enemies often drop bolts after they are destroyed , and these can be exchanged for various restorative items and upgrades . However , unlike in Mega Man 7 the security cavern offers a way to obtain large amounts of bolts without having to repeatedly visit stages . Some upgrades are unique to either character , such as Mega Man 's ability to call on his dog Rush to search for items , or an <unk> for Bass to combine with his wolf Treble to temporarily fly . Also distributed throughout the introduction and Robot Master levels are a collection of 100 data CDs that contain information on many prominent characters in the series . Most of the CDs are hidden either behind obstacles that need to be destroyed with a special weapon or accessed with a character @-@ specific ability , making it impossible to collect them all on a single playthrough . CDs collected in each playthrough are permanently placed in a database and remain unlocked after beating the game . Saved games are used in place of the series ' traditional <unk> system . 
