HIDDEN OPTIONS
On the Title Screen, choose Options. Highlight Continues and hold Run and Block (C-Left and C-Down are the default buttons for Run and Block) until a special options menu appears. To exit the menu, highlight Exit and press the A Button.

Options available to change:
Endings. Choose between On or Off. Default is Off. If you choose On, the game will automatically end after defeating the first Character in Arcade Mode and you can view the ending.
Fatalities 1. Choose between On or Off. Default is On.
Fatalities 2. Choose between On or Off. Default is On.
Level Fatalities. Choose between On or Off. Default is On.

HIDDEN CHARACTERS
There are several hidden kombantants in Mortal Kombat 4. To access them, select HIDDEN on the character select screen, then do as follows:
NOOB SAIBOT
After entering Hidden on the character select screen, press Up, Up and Left (the cursor will be on Reiko) and then press Run and Block together.
GORO
To Play as Goro, select Hidden on the character select screen, then press Up, Up, Up and Left (the cursor will be on Shinok). Press Run and Block together to play as Shinok.
MEAT
To play as Meat, you'll have to go to "Group Mode" and play as every character, and win every match. After you finish playing, pick any character, but when the match starts you will be playing as Meat. Meat has all the moves of the character that you chose.
Thanks to Daron DeVries For sending in this code!
To get Kitana you must select the hidden character button at the player select screen. Press "A" and go up to up to Lui Kang and hold block and run. This code only works in the N64 version.