Foils

In the effort of writing villains, I've come across the wonderful thing that is foil characters (opposites or contrasts to the protagonists). Now I have something to go off of for villains and their motivations and personalities. Do you guys use foils or have any really good foil characters? Do you contrast by making the protag and foil exact opposites or do you put them in similar circumstances with different decisions/outcomes?

My best foil (with as little spoiling/backstory as possible) so far is a side protagonist (kinda in the protag's main party?) and one of the antagonists. They both had well-off and pampered lives that came to an abrupt end. While the good guy learned to rely on friends and become better, the bad guy blames their friends and more or less turns to the dark side.

Ikr, I completely forgot that was a thing until I had to come up with the villains. After that it was surprisingly easy to think up backstories and motivations. I only have a few left that don't quite fit, but their foils aren't fully done yet either.

Those characters have the same means to an end (get crystals for different things). Foils tend to have more contrast in personalities, motivations, or even key decisions they make. They are similar enough to each other to be "linked" but have key differences that usually make the good guy stand out.
Here's a good link that explains a lot better and goes a lot more in depth than I can:
https://writingexplained.org/grammar-dictionary/foil

If you like RWBY there's been some foil posts floating around that have some really cool in depth analysis

Ooh, I love a good foil!
My favorite foils are probably Hamlet/Laertes.

Because Hamlet is constantly moping and thinking about killing his uncle but Laertes bursts in and threatens a coup right after his father is killed because he's a man of action.

Tybalt and Benvolio are also great foils.

My main character and her best friend are foils to each other in the way that they relate themselves to other people and the world. MC believes she has to always be correct and that backing down or admitting a mistake makes her look dumb, so she has this false confidence in almost every part of her life. Her bestie, on the other hand, doesn’t allow himself to have a solid opinion on anything and is very indecisive and hesitant due to how he bases his self-worth on what other people think of him. They both allow each other to move closer to the balance of healthy self-worth by teaching each other opposite lessons.

that sounds like a great dynamic to work with! That's a really good example of foils not being enemies. Foils work really well in friend positions too.