All Systems

Spike Slide
In the Kombat Tomb, if someone is uppercutted into the spikes in the ceiling, hold down on both josticks to fall from them.

"Hello"
If a player is uppercutted into the Dead Pool acid, hold down on the joystick to hear Dan Forden say Hi.

Play Classic Pong
Play in 2 player mode and win 250 battles and you will be warped to play a round of pong with your opponent.

No Throws
Hold Down + HP at the versus screen.

Random Select
At the select screen, press Up and Start at the same time.

15 Best Players
During the attract mode, hold down on one of the joysticks.

Fight Smoke
In the Portal Stage, uppercut your opponent.  When Dan Forden pops up and says "Toasty", press Down and Start and you will be sent to Goro's Lair to fight Smoke.

Fight Noob Saibot
Win 50 matches and you will be sent to Goro's Lair to fight Noob Saibot.

Fight Jade
In 1 player mode, reach the player under the ? mark.  During one of the rounds, beat the player using only LK and you will be sent to Goro's Lair to fight Jade.

At the Character Select Screen...
Fight Shao Kahn: F, U, U, F, B, Select
Fight Kintaro: U, D, D, F, F, Select
Fight Noob Saibot: B, U, D, D, F, Select
Fight Jade: U, D, D, B, F, Select
Fight Smoke: U, B, U, U, F, Select
30 Kredits: B, U, F, D, B, Select
Fatality Time Extend: U, U, B, U, D, Select
Super Strength and Defense: D, U, F, U, B, Select

Logo Trick: Turn on the Super NES and hold the L and R buttons down and push Start.

Battle Mode: At the title screen, hold the L and R buttons down and push Start.

Test Mode
Go to the Options Screen, place the cursor next to the word Done, and push B, D, B, F, D, F, B, B, F, F.

Toasty!
Use the Test Mode and choose Oooh Nasty.  A new face will yell "Toasty!".  This face comes up and replaces the "Toasty" Dan Forden head.

Fergality
Use the Test Mode and select Oooh Nasty.  Play as Raiden in the Armory, and when "Finish Him/Her" appears, press B, B, B, BLK.