here's a list
#1. Masked villains:
masked villains are the best(in my opinion) they are mysterious and unknown to all, which is a good thing, you shouldn't have villains be in the open so quickly like other stories does, it ruins the danger alert of the character,
masked characters make good big bosses, example: tobi, masquerade(bakugan).etc study on these characters and see how badass they are compared to other villain characters,
3. always let the character be in the shadows, as stated in 1, it's always good to keep the mystery and unknowns, have your readers bursting their brains trying to figure out who he is and what he is gonna do next,
also let him have a badboy persona to him, he shouldn't be serious like hulk, let him have a charm, a seductive personality that entices the heroes and the readers, now, I don't mean carefree like tobi,
just a CALM AND DANGEROUS persona.
another thing is, Don't and I mean DON'T let him reveal his identity anytime soon, keep the mystery for a very long time, because with the mystery status, he is literally an UNLIMITED character, you can have him do any move without someone saying ''he can't do that''
and the biggest of all, let the villain have a SENSIBLE GOAL, a goal that makes sense, don't make a joker sue, don't make him a
character who wants to take over the world for the fun of it, I personally dislike a character like that.
let him have a goal that HE thinks would be better for humanity,
there is the rebellious prince, where the masked man was once good, and saw his teammate's ideology to be corrupt and turns rogue to change it, speaking of rebellious prince,
it would be awesome to have a literal prince that want's to overthrow his dad and reign in his place, thinking it would cause peace
2. there is savior complex, where the masked man want's to change the world with his own ways rather than control it, however he views himself above others as being the one to save them all, which is opposite to the humble heroes