Key

From SMWiki

Super Mario World Sprite
Key
Sprite number(s)	80
Type	Normal sprite
GFX file(s)	GFX01 (SP2)
Palette(s)	8

The Key is an item Mario can pick up and bring to a Keyhole in order to activate a secret exit. Getting the Key to the Keyhole is often a puzzle, but it is sometimes used in place of a Secret Goal for it's quick exit, instead of having the Goal Point routine (which makes the key and keyhole setup work much smoother, especially in tight places where Mario would be running into a wall, etc...).

Advanced players can glitch the key due to they being able to both jump and pick it at the same time, the so called Key Jumping. This also works due to the fact that it is, basically, a portable platform. However, this technique should never be required to beat a level. It's unfair, and, most of the time, requires use of slowdown

The key is sprite number 80 in Lunar Magic.

Unused Flying Key Sprite?

In Super Mario World, there is a game genie item reserve cheat code that can spawn any item in the reserve box. By changing the last 2 numbers to any hex number will spawn a random item. However if you input the following code, 7E0DC20D (Pro Action Replay), the item in the reserve box will look glitched, but, when released, will be a flying key. However, for some reason it hurts Mario when he touches it. It can't die, and Mario can spin jump on it. It can become a normal key, if Mario touches the key when Mario has star power. Yoshi can also eat it, and when spat out, it can turn into a normal key as well. It is unknown whether the flying key was a sprite Nintendo hadn't finished coding and forgot to take out of the final product, or a glitched object that uses other object pointers, as it doesn't show in Lunar Magic's Sprite Window, nor does it appear as any unused objects with Lunar Magic's Add sprite Manual command.

There is a Custom Sprite version however, for those who want to use a flying key.