FLAT ESCARDOS is an UNDERCOVER DEMON?! | Fate Strange Fake Episode 8 REACTION!

Many servant can be in more than one class and often the different classes represents different aspects of the hero.
For example Gilgamesh can be an archer and a caster, archer is him as a tyrant while caster is the enlighten king he becomes at the end of his tale.

The Jack the Reaper in Strange Fake represents all the crazy rumours and legends born of the murders of the real Jack the Reaper so he is sort of formless and could qualify for most classes. However, the madness from the Berserker class kinda cancels out his innate madness leaving fairly agreeable. In the novels Jack explains that if he had been any other class he would have possessed Flat and gone on a murder spree.

We do see assassin Jack in other Fate series but they're quite different since they're the real Jack mixed with the rumours so they have a body and a very different personality.

5:52 he didn’t make the sword the sword caster had was the sword the police confiscated off of Richard.

Any servant can appear as any of their compatible servant classes, depending on what part of history you pull it out from.
Heracles can ANY class but Caster, because he doesn't use magic. Obviously.

You have to crazy specific and conflating one servant to a single class because that's how you remember them in one Fate anime isn't gonna treat you kindly in other Fate media.

For example:
Saber. Which one?
There are many Sabers. Any one who used a sword or a bladed weapon, figuratively or literally, can be classified as a Saber.

Then Artoria. Which one?
There are many versions of her, in different classes. Including Proto Saber.

Saber Artoria? Which one?
Regular Saber Artoria? Or Saber Alter?