Super Metroid
Super Metroid
Metroid - Did You Know Gaming? Feat. WeeklyTubeShow
Present near the beginning of the ROM is a hidden message:

Special thanks
Genji Kubota
all debug staff.

It is not known whether this line can be displayed in-game. It seems to simply be something added by a programmer as gratitude toward the debug team.
Contributed by MehDeletingLater
Through the use of cheat codes, an early AI for Shaktool can be accessed that moves considerably slower than in the final game, and also features an unused attack fired from its head that deals a small amount of damage.
Contributed by MehDeletingLater
Right after Samus acquires the Morphing Ball, two Eye security cameras in the first room of Brinstar turn on that are implied to alert the Space Pirates that Samus has arrived on Zebes. As Samus travels further into Brinstar, the rest of the planet "awakens" and becomes swarmed with enemies, causing the Eyes to disappear for the rest of the game. The Eyes shine a yellow light that tracks Samus around their immediate area when she is near them, and they shut when she walks far enough away. Once Samus searches back around into a corridor in Crateria's central rocky cave, a small Item room featuring a Chozo statue holding a Missile Tank can be found on the left side. This Item room can only be accessed using Bombs, and under normal circumstances, there is nothing of note about the statue.

However, should this room be entered early through hacking or the "Spacetime Beam" glitch that resets item and boss placements in the current save file, the room will be dark and the Chozo statue will have nothing in its hands. When Samus walks close enough to it, the statue will shine the same yellow tracking light to that of the two Eyes and the room will brighten, suggesting that there is an Eye hidden in the statue. This Eye appears to behave the same way as the other two and disappears for the rest of the game once the planet awakens. While the X-Ray Scope does not reveal anything underneath the statue, through the use of a glitch technique that replicates the effects of the Spacetime Beam while creating numerous graphical glitches (most notably in this case causing Chozo statues to become transparent), returning to the Item room will reveal the hidden third Eye. This Eye has some different properties compared to the other two, such as having a blue eyeball rather than red, and will turn around and close when Samus walks far enough away rather than just closing where it is.

This Eye is likely an earlier version of the Eye found in the final game that was originally intended to be found in normal play at the start of the game and eventually scrapped, but was left intact, possibly because all three Eyes eventually disappear anyway, and was not intended to be found by players.
Contributed by MehDeletingLater
Crocomire's tongue is a separate enemy that can be killed, but in normal gameplay it is practically impossible to do so as killing it requires the use of 83 Power Bombs (93 if the Crystal Flash is performed). Normally, the game caps off the number of Power Bombs you can have at a time to 50, with the game's speedrunning community deducing that either glitch techniques must be used to acquire more Power Bombs, or you must rely on the 4% drop rate for items dropped from Crocomire's projectiles in order to get more.
Contributed by MehDeletingLater
According to a Game Shokunin Vol. 1 interview, with game's enemy programmer Yasuhiko Fujii, before the boss fight against Draygon, the player will encounter a group of Evir enemies that do a little “dance”. Their movements actually spell out the words “Keiko Love” in English. This idea came from a girlfriend he dated, name Keiko. Fuiji was busy with work, and couldn't make time for Keiko, so when everyone in the office was asleep at night, he snuck this Easter egg into the game. There were never little Evir dance written in the game's planning documents, so he remembered his heart racing fast as he coded it. However, the team's staff had no knowledge about it and never discovered Yasuhiko's code in the game.
Contributed by ProtoSnake
Originally it was planned that, upon death, Samus would scream as her suit would explode to reveal her naked body. However, when the game was released, Samus was given clothes and her scream (recorded by composer Minako Hamano) was removed after being deemed too sexual.
Contributed by Ophl
During the Ceres Space Colony fight with Ridley, hitting him enough will cause him to fly away. At the same time, he will drop the baby Metroid to the ground, before coming back down to pick it up. He will then fly away as normal and the self - destruct sequence begins as usual.
Contributed by mathwiz86
Entering the room that contains the Golden Torizo in Ridley's Lair while holding down the face buttons on the controller will trigger a secret debug code. There is a catch, however: once you let go of the fire button, the game will freeze due to two of the beams being incompatible, but being forcibly enabled by the code. As such, you can enter this room while in Morph Ball mode to avoid freezing the game or just be lucky on how you let go of the fire button.

This will reset your inventory to 700 Energy, 300 Reserve Energy, 100 Missiles, 20 Super Missiles, 20 Power Bombs, all beams equipped (remember to disable at least one of the bottom two), and all items except Screw Attack, which is obtained after fighting the Golden Torizo.
Contributed by KidDivinegon
There's an alternate way to kill Draygon, the boss of Maridia. Destroying the cannons on the wall will cause electricity to flow out of the walls. If you grab on to the electricity with your Grapple Beam while Draygon is holding you, the electricity will flow through Samus and into Draygon, killing her in a few seconds.
Contributed by Pogue-Mahone
At the time of Super Metroid's release, it was the largest file size on a cartridge ever released for the console at 24-megabits.
Contributed by ThisGuyInTheSuit
At the very end of the game, Spoiler:you can save the creatures who taught you the Wall Jump (the Etecoons) and the creatures who taught you the Super Boost Jump (the Dachora). You can save them during the self-destruct sequence after beating Mother Brain.

Spoiler:These creatures are present in Metroid Fusion, which takes place after Super Metroid, suggesting that saving the animals occurs in the canon ending to the game. This time they save Samus from the explosion of the station.
Contributed by pAroxizm
The Etecoons who teach Samus how to wall jump sing the power-up theme before their demonstration.
Contributed by peanutgamer
Samus Aran's appearance in Super Metroid was based on the actress Kim Basinger.
Contributed by DidYouKnowGaming