Key

Keys are used to open locks. Keys typically only open one door; once that door has been accessed, the key has no further use.

Appearances

Blaster Master

Fred guards the Key needed to access Area 5.

Blaster Master: Enemy Below

A key is needed to access each boss chamber. Each Area typically features two catacombs, one with the Area's key at the end, the other with its boss.

Blaster Master Zero

“	A key that opens the shutters in the Waterworks Area.”
	— Key 1 • Blaster Master Zero

As in the original game, the Key needed to get to Area 5 is guarded in the depths of Area 4 by Ribbiroll. This key, listed in the Pilot screen of the Menu as "Key 1," unlocks both a shortcut back to the top of Area 4 and the exit access to Area 5.

“	A key that opens a shutter somewhere in the Mutant's Inner Body Area.”
	— Key 2 • Blaster Master Zero

Additional Keys being necessary to access boss chambers is revisited towards the end of the game: Key 2 is guarded by Antibody Cell in Area 8, immediately due west of the shutter it unlocks on the path to the Mutant Lord. Keys 3, 4, and 5 are hidden throughout Area 9, required to open a triple shutter blocking off the game's final setpiece.

“	A key that opens a shutter somewhere in the Alternate Dimension Area.”
	— Key 3/4/5 • Blaster Master Zero

Blaster Master Zero 2

Areas gated by keys return in Blaster Master Zero 2, with a frequency approaching that of Enemy Below.

A lesser form of key appears in certain top-down dungeons, collectible from breaking blocks or defeating certain enemies. Collection of these keys is not tracked in the Menu, but a persistent count is kept for each dungeon that contains and requires keys. These keys are technically reusable, with passageways gated off and marked with multiple locks corresponding to how many keys must be held to pass.

Access Keys also exist as a major collectible, awarded for defeating planet bosses or completing other major objectives. These are used to unlock Dimensional Tunnels on the Space Map, opening up travel to new planets and planetoids. Collection of up to a total set of 6 of these is tracked on the Pilot screen in the Menu.