I think one character people don't give much thought to, but is a genuinely plausible pick, is M. Bison from the Street Fighter series. He's a rare situation where, like, his moveset actually has a lot of potential, but at the same time, could be quite simple to think up. Here's my own concept for his Specials, at least:
Neutral B: Psycho Shot. Acting as a projectile, I think this one is pretty interesting. Though it's a little similar to how Hadouken works with its speed being able to be controlled by the input, I think that doing the input for it should have it work a little more like Psycho Cannon - moving slower, but with a bigger hitbox and a multi-hit property as well as big damage.
Side B: Psycho Crusher! Having Bison prepare himself before launching sideways, coating himself in Psycho Power, I think it would be a good move if it multihits opponents that it hits, as well as being able to be aimed slightly upward or downward when used on the ground (and being a good recovery tool in the air.) Inputting the correct command gives it a little more power and range.
Up B: I think this should be Bison Warp. Being a teleport, some might think of it as unoriginal, but I think the interesting difference here would be that, compared to say Mewtwo or Palutena, it has slightly shorter range - but significantly less end-lag, as well as being able to act after it (though it can only be used once in the air.) When on the ground, it works a little more like a counter of sorts - taking the form of Hell's Warp, using it "through" an opponent puts them in a stunned state, allowing you to punish them with low end-lag. However, it requires a read - long start-lag makes it unsafe on shield.
Down B: In this case, I'd like to suggest Devil Reverse. Acting a little like ZSS's Down B, this has Bison leap into the air, but if you don't make an input, it essentially turns into Head Press on the other side - which is a spike that can bury opponents on the ground. However, it's also possible to cancel it by tapping B again, which has Bison activate the Reverse - stopping his momentum forward and having him bring a fist down coated in Psycho Power, which actually also has a spike on the initial swing - as well as doing minor damage for a short time! This can also be used as a recovery move, as it doesn't leave you vulnerable after use - in fact, you could even use your double jump out of it!
Lastly, his two Final Smashes would be the Nightmare Booster when close-up, or the Final Psycho Crusher when at longer range from an opponent.
Mostly because he is my SF main and he has a theme I really want to see in.