Enter these on the Password screen of the original Metroid (which you unlock by beating Zero Mission).

111 Missiles, 4 Energy Tanks, Ice Beam, And
No Suit – BOMBS_ MISSLE SCREW_ ATACK_

All Upgrades, Unlimited Missiles, And
Health – NARPAS SWORD0 000000 000000

Morph Ball And Bombs – 000000 000000
4G0000 00000H

No Suit – 000000 000020 000000 000020

No Suit And Wave Beam – 999999 999999
KKKKKK KKKKKK

No Suit, In Norfair, Infinite Missiles, And No
Upgrades – SAMUS8 RIDLEY 444444 444444

No Suit, 255 Missiles, And Fully Upgraded –
JUSTIN BAILEY –––––– ––––––

On Track To Finish With Best Ending –
X––––– ––N?WO dV–Gm9 W01GMI

Ridley’s Lair, Not Very WellEquipped –
GameIN FORMEKMagazi ne000W

Ridley’s Lair, Well-Equipped – AndyMc Namara
GiEdit or 03Y

Zero Mission Endings
Fulfill these requirements to unlock the corresponding art of Samus.

Blue Jumpsuit – Beat Normal or Hard in under two hours with more than 15% completion

Close-Up On Her Face – Beat Hard with less than 15% completion

In Shorts At A Bar – Beat Normal in under two hours with 100% completion

In Shorts At A Window – Beat Normal with less than 15% completion

In Shorts In A City – Beat Normal or Hard in over two hours with 100% completion

In Shorts Overlooking A City – Beat Hard in under two hours with 100% completion

No Helmet Enjoying A Sunset – Beat Normal or Hard in three hours with more than 15% completion

On A Rock – Beat Easy, or beat Normal or Hard in over four hours with 100% completion