Go West, Young Superman

What would you expect in a Western flashback story in a superhero setting?

I'd expect to see some or all of these, depending on what kind of superhero series the Western adventure happens in.

Historical figures from the era, and possibly folklore characters as well.

Western heroes from the comics (who often emulate Western heroes from other media when they were created) who are usually skilled normals because active superhumans are presented as rare before the Golden Age in-character as well as in print.

Masked vigilante heroes (like the Lone Ranger and Zorro, Marvel’s Phantom (formerly Ghost) Rider and DC’s original Vigilante) who are either skilled normals or mildly superpowered.

Human Western villains (outlaws, corrupt authority figures who rule isolated towns) or maybe slightly superhuman ones.

Steampunk and/or other super-for-the-time technology.

Monsters, possibly drawn from local mythology or from 19th century literature like vampires, or a Western horror crossover like a ghost town with actual ghosts.

Cameos by superhumanly long-lived characters (such as Wolverine or Vandal Savage), time travellers, or someone else the PCs might have ‘previously’ met in the future, if the PCs don’t qualify for this themselves. If the PCs are time travellers they might meet a legendary hero or villain they've heard stories about, or a long-lived character they know from their present, while long-lived PCs having flashback episodes might meet time travellers instead.

Prior and ‘reverse’ legacy characters, if a PC is established as part of an ongoing group they might meet either established or previously unmentioned earlier members (like the modern Ghost Rider meeting a Wild West Ghost Rider, unlike the aforementioned Phantom Rider), including regular non-powered ancestors (like Superman looking into his adoptive family’s history and discovering the time a Kent ancestor fought opposite Jonah Hex).