How would you go about creating a unique rogue’s gallery for a legacy character like X-23 or Kamala Khan? As much as I love them, they lack memorable archenemies or in Laura’s case, they just recycle the trigger scent.

I mean, I think the cockatoo is pretty memorable…

It’s the same for creating them for any other hero: 

1. You need a good, memorable concept. Don’t just pick random objects, add the word -Man onto it and call it a day. People make fun of Stilt-Man for a reason.
2. That concept needs to work with that specific hero. The purpose of the villain is to be an antagonist for that particular hero/protagonist, so the villain should at the bare minimum make sense in terms of power levels, location, and so forth. Beyond the bare minimum, you’re looking for thematic resonance – while “dark mirror” villains are popular, you don’t necessarily need one, you just need the villain to do stuff that would grind that hero’s gears in particular. 
3. Don’t one-and-done the villain. One of the things that make villains “classic” or “memorable” is that they have a long history with the hero, which builds up tension between the two of them and really gives them a reason to go at each other.  

TBC…