“Evil” is quantified by the protagonist making a deliberate choice to go against or betray their past allies or beliefs, and is actively treated as a villain by most of the cast or world. This includes morally gray routes where the protagonist still has good intentions but is taking on an antagonistic role.

I will only be including games where the choice to become evil either happens very early on or atleast makes up 1/3rd of a single playthrough. This excludes any game where the player is offered a binary choice before the final battle, because up to that point the player is forced to play the hero. Games where the only option is to be evil are also not included.

I cannot comment on my own posts anymore because backloggd softbanned me, feel free to leave recommendations and details so I can have more games to play like these :)

Not included:
Shin Megami Tensei Nocturne: Route contains all of one boss battle and you hardly feel like you're even doing anything bad, it's the game's true ending.
Tactics Ogre: Small branch in the middle of the story caused by slaughtering a town of innocents for a kingdom. Killing isn't immoral, moving on.
Mass Effect: same reason as any other WRPG, lacks actual routes and just has choices that don’t go anywhere.