Mario Is Missing! (SNES)

Bowser battle
Select the "Continue Search" option at the title screen. Seven spheres will appear. Enter ZPF*M86 as a password to reach Bowser, the final Boss. To view the ending sequence, the Boss' head six times. Leave through the door that the Boss used to enter, then find and free Mario to complete the game.
Room Codes

Door First room Second room Third room
First door
PVV23CZ
CX746YF
DWV6P78

Second door
FCBSB6W
NBGR6CF
PCD1384

Third door
YHYAMLZ
XIKRN4X
DJ49LZ3

Fourth door
Y4MOPFW
X**KLDK
D9FKPTR

Fifth door
G5F96CX
S48O5N4
TTMGMQM

Roy battle
Enter JPF13HT as a password to advance to face Roy, the last Koopa. Hit him six times to reach Bowser.