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.
This is hilariously lampshaded in Death Battle when Wiz and Boomstick immediately discard this movie from memory when they came across footage of Shao Kahn changing into a Hydra. Keep in mind that Death Battle is usually pretty liberal with its source material, but it appears that even they have their limits.
Wizard: Shao Khan can also access his inner beast to transform into...this thing.
Boomstick: Quick! Make me forget that shit!
Wizard: Right! (screen fades to white) Never happened!
Pandering to the Base: Annihilation vomits new character after new character at the audience in an attempt to fit in all the new arrivals from Trilogy and earn some cred from the faithful. General feedback on the movie should be an indication of how well this worked.
Snark Bait: The movie is so horrendously bad, that much of the entertainment can be derived from making fun of every single thing that's wrong with it.
Plus the... flying creature that emerges from Shao Kahn's body after he's beaten. Neither it nor the body husk it leaves behind is any believable.
On a related note, the gargoyle that appears is arguably either the film's best effectnote which is saying a lot, or is worse than either of the creatures in the aforementioned fight scene.
When it grabs Sonya at one point, she too becomes a rather obvious CGI double.
Ermac's mask falls off during the fight between him and Sonya. This bit occurs when the latter grabs the former's head with her legs.
A similar event happens during the fight between Scorpion and Sub Zero. Only this time, it occurs when the former catches the latter.
When Liu Kang does his flip kick, there's a visual flash of when he kicks the camera.
Rain gets knocked into a flaming pit by Shao Kahn. When Baraka gets knocked towards the same pit, we see... Rain falling in again.
There are cables visible all over the place, but none more noticeable than during Scorpion and Sub Zero's fight.
Motaro's front legs are obvious human legs with human feet instead of horse legs with hooves.
In other words, pretty much everything. Even the titles are bad by virtue of reusing the titles from the original movie, as explained below.
They Just Didn't Care: They use the exact same title sequence than the first film, with the only change being that the letters of "Mortal Kombat" flip to reveal the subtitle. What's more, they reuse clips from the first movie in several places.
See also the Rain example above.
Video Game Movies Suck: Even compared to other video game movies this one has an especially awful reputation, with more than a few regarding it as the worst game adaptation of all time... or at least the worst one that Uwe Boll didn't have a hand in.