These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Quan Chi. The creators just love this guy, and so do a lot of fans.
Sareena, who is most likely the best example of this next to Quan Chi. Despite debuting in an unpopular spinoff, there was quite a bit of fan interest to see her return for future games. After several attempts to make it into the series proper, she's finally made playable in Armageddon, where she proves to be a valuableally of Younger Sub-Zero and is made into a top-tier character.