■Shadow Noob Saibot - A homage to the original secret characters. He is found in The Cathedral. If he is seen standing in the background of the stage, the player must win both rounds without blocking. Noob Saibot will then proceed to fight with the player, appearing much stronger than the other ninjas.

■Klassic Reptile - A homage to the original secret characters. He is found in The Pit Stage. Very similar to the MK1 requirements, a shadow figure must go across the screen, and the player must win with two flawless victories in a row, and with a stage fatality. A loading screen will then appear, and the player will be transported to The Pit Bottom fighting Klassic Reptile.

■Klassic Smoke - He is found in Living Forest. Like the other two, this character pays a homage to the original secret characters, but unlike the other two, once you press Select+Down (Playstation 3) or Down+Back (Xbox 360), the opponent will be taken out and he will fight you himself.

■Klassic Jade - She is found in Goro's Lair. To fight her, you must beat the tournament ladder, up to Shang Tsung, with all flawless victories. You must then defeat Shang Tsung with two flawless victories and a fatality. You will then be transported to Goro's Lair, and fight Klassic Jade

IMHO
for noob, I waited for one whole round until the 2 shadow priest with a hostage arrive in front. Then the second round, noob saibot was standing on top of the stairs... 

For reptile, the shadow figure is somewhat like the santa claus in the movie flying. It is from the right swirly to the left after about 4-5 seconds into the fight. If you have problem perfecting the 2 rounds, try the scorpion's method.. jump back, spear, combo (make sure this is a combo that sends your opponent flying back across the screen... then spear again, rinse and repeat. And don't forget to do the stage fatality.. Try characters that uses block for stage fatalities

for smoke, as its hard for me to find him by looking for him through the trees, I just press select and down randomly when I reach this stage...

for jade I didn't get this one yet  ... the requirements are pretty strict however... I think you can try the scorpion method, otherwise, just use your most favourite character that you can muster... You must win 2 rounds flawlessly, every single round up to shang tsung and win 2 flawless round with him and finishing him off with a fatality  ... I have some trouble perfecting every opponent.. as even on beginner, some of the characters always seems to be able to land one or two punches at me  ... gonna try again tonight