Kung Lao singlehandedly taking out the duo of Shang Tsung and Quan Chi. Keep in mind that in the original timeline, those two mopped up Kung Lao and his companions. Furthermore, Kung Lao bests Kintaro immediately afterwards.
The game actually got awarded best fighting game of the year in an Australian gaming magazine despite being banned there. That's how well-received it was.
Even better: thanks to the new R-18+ rating for games, as of May 1, 2013, MK 9 has been un-banned from the land down under. But we don't get the normal game, oh no: we get the Komplete Edition.
In the finale, a rejuvenated Raiden channels the power of the Elder Gods and kills Shao Kahn, possibly for good.
Sindel slaughtering most of the heroes without breaking a sweat. Really sets the tone for the finale, a warning that things are going to be VERY different.
Sub-Zero's ladder ending where he and Scorpion join forces to easily defeat the Lin Kuei who murdered both of their families, and proceed to basically become The Dreaded for anyone who kills the innocent. People have wanted to see something like this for a while, and now they did.
After Raiden accidentally kills Liu Kang, and Shao Kahn steps onto Earthrrealm in triumph, Johnny and Sonya decide they are going to go down fighting. Fortunately, they survive.
The reveal trailer for the PS3 version's guest fighter is awesome itself. It shows Scorpion and Sub-Zero fighting as Shao Kahn watches. Scorpion gets the upper hand and Shao Kahn orders him to finish Sub-Zero off. Just before Scorpion can, however, another blade impales Sub-Zero from behind and drags him off screen. Scorpion watches this new challenger approach... And it's none other than the Ghost of Sparta himself, Kratos, brandishing his Blades of Chaos as he prepares to do battle with Scorpion.
And the reveal trailer for the final DLC character. It shows Sub-Zero, Scorpion, Quan-Chi, and Kano's intros as they stare at an unknown opponent. Then in a blaze of fire, Freddy Krueger appears, letting out an evil laugh. The trailer shows off several of his attacks, some of which are based on his most famous kills throughout the Nightmare on Elm Street films. Special mention goes to his fatalities, based on the ways he killed people from the first and fourth films.
Just the fact that this game propelled the MK series into the competitive scene is already a fucking amazing achievement. Seeing it standing up there with the likes of Street Fighter and Marvel vs Capcom is really something the guys at Netherrealm should be proud of. Granted it died down quickly, but still.