Sound Play is a sound test for the game, letting you play various tracks from the arranged soundtrack. There are a few different ways to play a track, A standard method is available, but if you want you can also pick the "manual" option, which lets you choose a track and character.
Once you've picked your music and character, a brief load screen will show their stage, then the music track will start playing and a picture of the chosen character will be shown. Finally, there's also a random selection, which will pick music randomly and display random characters from the game. The characters will go through their sideline animations.
In addition to the sound test, the "option" menu is actually a gallery mode. There are four selections to choose from. The "art file -demo-" lets you view sprites and backgrounds from the game's cutscenes. The "art file -ending-" is the same kind of thing, but for the game's ending sequences.
The third gallery is "chara data -new character-". This gallery contains some images of Vice, Mature, Chizuru, and Goenitz. Some of the drawings show early versions of these characters, including completely different outfits for Chizuru and Leona which were not used in the final game, the links were gotten from https://rq87.flyingomelette.com/RQ/KOF96C/nc.html.
Vice & Mature arts:
And finally, the fourth gallery is "chara data -etc-". This gallery contains drawings of various characters, several of which appear to be scrapped fighters who didn't make it into the game, the images were gotten from https://rq87.flyingomelette.com/RQ/KOF96C/etc.html.
Some characters that appeared in the game appear with some unused images of the game below
-The sixth image shows a character with the Kusanagi clan's crest on the back of his shirt, but is clearly not Kyo. Perhaps it's Saisyu but his face looks a bit different.
-The seventh image shows a character who resembles Shingo Yabuki, who wouldn't debut until The King of Fighters '97.
-The eighth image shows an unknown character, who slightly resembles Axel Hawk from Fatal Fury 2, but I doubt it's meant to be him.
-The ninth image shows an unknown character.
-The last image shows an unknown character, although perhaps it was an early design for Chizuru.