6. The Mirror Antagonist
Though an extremely common trope in video games, the "mirror antagonist" is also relatively prevalent in movies and TV, especially in the superhero and fantasy genres.
If a game's designers can't come up with an interesting look for the villain, why not just imitate the hero but give him a sinister spin?
And so, countless video games have created antagonists who are basically polarity-reversed iterations of the protagonist, such as Mario's frenemy Wario, who not only looks like Mario's evil twin brother but his name also basically means "Bad Mario" in Japanese. Sonic the Hedgehog's Shadow the Hedgehog is also much the same.
In more literal examples, Devil May Cry's Vergil is Dante's older twin brother and Crash Bandicoot 3's villainous Uka Uka mask is the mischievous brother of your Aku Aku mask.
While it's easy to dismiss the yin-and-yang approach to villainy as lazy and desperate, it can also be a fun way to literalise the protagonist's own internal struggle, by having them face off against a foe who so blatantly resembles themselves.