Following up on Brandon’s comment, videogame bestiaries are a huge one for me. It’s also one of those things people used to complain about, like the different Castlevanias reusing the same monsters, but at the end of the day, having a franchise that builds upon itself and keeps bringing back older material translates into building an aura and constructing a legacy that will be remembered for ages.
This is something Pokemon has understood perfectly, and, I think, one of the main reasons of its popularity. Just imagine if they had forgotten about Pikachu after the first entry. Another great example of a franchise having a more clearly defined personality thanks to recycling material is Shin Megami Tensei, and that is because Jack Frost, Angel and Apsaras have been there for a while now. Same goes for Dragon Quest and so many other sagas.
I love videogame bestiaries, they are often the greatest ways to showcase the creators’ imagination and such a powerful vehicle for storytelling, world building and defining the texture and atmosphere of the game when used properly. In so many cases the baddies end up being more iconic than the protagonists themselves, think of Star Wars and how the stormtrooper’s design has ended up being a lot more iconic than the random dude in a bathtub robe attire of jedis.