Oh and Quan Chi and whoever was gonna be planned as DLC

Harley Quinn was. What about Doomsday?
Johnny Cage: Nutpunch to the max
Kung Lao: Hat saw to the chest (like with Baraka in MK4)
Robin: An arrow to the knee... "Feel the pain!"
Martian Manhunter: Become invisible and torture
Mr. Freeze: Freeze the victim's head and kick them
to the ground, resulting in the head exploding
The Penguin: Penetrate the umbrella to the throat with an evil face
Quan Chi: Rip off the 1st MK9 Fatality for him
Harley Quinn: Offer a lethal poison drink to the victim
Doomsday: Whack the opponent with superspeed
and strength like in Trilogy, to the death
Superben, you must introduce yourself in here immediately. You will obtain valuable information from there and become more known to MKO.
Wonderful Regards,
Zmoke the Finn

Zmoke, your ideas for Mr. Freeze and Quan Chi sound like M-rated Fatalities. T-rated fatalities must have no dismemberments or amputations of any kind. At least, that's what I think, judging from MK vs. DCU's T-rated Fatalities.

Reptile:
-Fatality 1- Showers the opponent in acid, leaving them a green acid-stained skeleton. (Covers the opponent completely in acid, doesn't show their flesh and muscles dissolve.)

-Fatality 2- Performs his first MK9 Fatality. (Only Reptile doesn't rip out the opponent's stomach, he just leaves the opponent to die from the acid.)

Quan Chi:
-Fatality 1- Trances his opponent and forces the opponent to break his/her own spine. (Like Dairou's Hara-Kiri, only without a blood-pool forming.)

-Fatality 2- Breaks both of the opponent's legs with 2 swift kicks, then summons a giant skeletal hand which crushes the opponent on the ground with its palm. (The palm stays on the opponent, no blood-pool forms.)

EDIT:
I'd sort of like for the MK heroes to have 1 Fatality and 1 Heroic Brutality. Zmoke's idea for Johnny Cage, having Johnny repeatedly assault his opponent's genitals, could be great for a Heroic Brutality. It doesn't kill his opponent, but it would probably make them wish it did.

Joker - He walks up to the opponent and shakes his/her hand. The Announcer says "FRIENDSHIP?" and then we get a close up of the opponent as his/her skin turns white, hair green, eyes roll back as a wide grin is stretch across their face as they stumble forward dead. Then we move back to the Joker shrugging his shoulders as he reveals a thumb tack on his hand. Announcer: "Fatality."

Black Adam - eye poke of pushing a man's face through his skull of doom.

Superman - walks up to the opponent as he laser beams the opponent's head, then stops. The opponent collapses to the ground as some drool dribbles out.