The Mortal Kombat games were becoming stale in the mid-2000s with entries like Mortal Kombat: Armageddon and Mortal Kombat VS DC Universe. Since Armageddon essentially killed every character and the other was a non-canonical crossover, there wasn't much room for a sequel.
So, Netherrealm Studios made the choice to reboot Mortal Kombat by featuring a new timeline. A timeline in which characters were trying to prevent Armageddon from ever happening. As a result, many new events happen in this second timeline of three games that introduced many new characters.
Cyber Sub-Zero
In the first timeline, Smoke is converted into a Cyber Lin Kuei. However, due to altering the timeline those events never happen but time bounced back and bestowed that fate upon another. The younger brother Kuai Liang, the second Sub-Zero is betrayed by his own clan and converted.
This results in Kuai Liang becoming Cyber Sub-Zero, a new but quickly beloved Cyber Ninja. Later, Cyber Sub-Zero would regain his free will only to be killed by Sindel. His appearance in Mortal Kombat (2011) was so popular he became a secret variation for Triborg in Mortal Kombat X.
Skarlet
The red-clad Skarlet has an interesting history. Reports of a glitch that turned Kitana red in the original Mortal Kombat II resulted in fans calling this sprite a hidden character. This was not the case but the idea was so beloved by fans that when Mortal Kombat (2011) a.k.a. Mortal Kombat 9 came, Netherrealm used it.
So Skarlet ended up becoming an Easter egg in Mortal Kombat 9's Koliseum stage only to become a DLC character later on. Skarlet would make her biggest return in Mortal Kombat 11 with a unique design and an emphasis on her blood magik, fleshing her out into a new fan favorite.
Ferra/Torr
Easily the most forgotten new character of them all; Ferra/Torr is a girl and a beast who share a symbiotic relationship. Not much is told about them but they are loyal to the new emperor: Kotal Kahn. Ferra is voiced by Tara Strong who many might know as the voice of Harley Quinn in many projects including Netherrealm's Injustice series.
Ferra/Torr was introduced in Mortal Kombat X but did not get to return in Mortal Kombat 11. Fans did not take to the characters even if it was a unique idea. Perhaps they just need a proper revamp as some others got in the sequel.
Erron Black
When the idea of a cowboy ninja first appeared, fans did not know what to expect. However, Erron Black quickly became a beloved anti-hero for his downright overpowered gameplay. The mysterious nature of the character and the voice of Troy Baker was just icing on the cake.
Fans loved Erron Black so much that he received a much more balanced return in Mortal Kombat 11. The only gripe about Erron Black is that apparently, he has been around since the first tournament. This is a retcon that doesn't make much sense since he was never seen in Mortal Kombat 9.
Kotal Kahn
At least Kotal Kahn's retconning into existence made a little more sense; he was locked in Shang Tsung's flesh pits and experimented on only to be released when Shang Tsung died. Kotal is an interesting neutral character who rules Outworld strictly but he's not a soulless monster like Shao Kahn.
Kotal Kahn's Aztec design combined with his heavy brawler gameplay made him into an instant classic. He was done arguably even better when he returned in Mortal Kombat 11. There was even an Easter egg of him in the 2021 Mortal Kombat movie.
D'Vorah
Everyone's favorite yet controversial Netherrealm addition. D'Vorah as a whole was loved before she even debuted. Monster characters tend to grab gamers' attention more than humans so an insectoid woman with different bug-related abilities had everyone hooked.
What made her controversial are her actions in the stories of Mortal Kombat X and Mortal Kombat 11. D'Vorah cares only for her hive so she will side with anyone and kill anyone to ensure her hive's survival. This leads to D'Vorah killing several beloved characters including Mileena, Baraka, and even the poster child himself: Scorpion. So fans both love and hate the character.
Kollector
D'Vorah introduced the species known as the Kytinn meanwhile Kollector was players' introduction to the Naknada. A six-armed race where they are not given names, only titles and the one in Mortal Kombat 11 is Kollector. He is an insatiably greedy creature that taxes and collects everything people have for Shao Kahn.
Like with D'Vorah, Kollector was a new monster fighter that had everyone curious. Gameplay-wise, he was a new beast who could attack from any range and deal insane damage per second. Unfortunately, Kollector suffered from little development much like Ferra/Torr.
Geras
A construct and living weapon of the Titan known as Kronika made from the sands of time. Geras is a fixed point in time which means every time he dies, he comes back to life only stronger. With glowing eyes, haunting voice, unique design, and immortality: it's impossible not to ire him.
Geras is very reminiscent of both the T-800 and the T-1000 from the Terminator franchise combined. Though his gameplay contains very overpowered special moves, he was still a surprise addition. In the story, he was so powerful that the only way to stop him was to leave him in an endless void. A shame that Geras likely will never return in future games.
Cetrion
Throughout all eleven main games, the presence of the Elder Gods is always there. Through mentioning, through advice for Raiden, or even assisting in stopping Shao Kahn. The Elder Gods have always played a factor in the lore and it's surprising it took until Mortal Kombat 11 for one to become playable.
Cetrion is the Elder God of virtue and light who can control the elements in any way. Unfortunately, she is also a loyal daughter to Kronika, the main villain of Mortal Kombat 11. Cetrion has made a name for herself in the online community as one of the most overpowered characters on the roster. Much like Kollector, Cetrion can hit from any angle using her powers and using with devastating damage.
Kronika
Above the Elder Gods come the Titans and one of those Titans is Kronika, the Keeper of Time. She is the mother of both Cetrion and Shinnok, some of the most powerful villains in Mortal Kombat. Kronika broke the timeline, intending to restart history to reshape it to her idea of perfection.
The heroes of Mortal Kombat were able to defeat her once, thus allowing Liu Kang to become the new Keeper Of Time. However, she was smart and so the heroes had to time travel to defeat her a second time in order to get her crown. This marked the end of the second timeline as Liu Kang restarted time once fully in control of Kronika's hourglass.
