Reset dens and farm away
Almost everything in Hogwarts Legacy is linked to the collection system: which ultimately funnels into the platinum trophy. Shiny beasts are different, in that they’re more of a self-imposed activity that you can engage with if you so choose. Here’s what shiny beasts do (hint: nothing outside of bragging rights), and how to farm them.
What are shiny beasts?
Shiny beasts often have a unique appearance, and have a little star next to their name. They’re an extra activity you can engage in: to have all of your beasts of shiny rarity.
You can tell a beast is shiny by investigating them thorough the inventory menu, or by viewing the star above their name in the overworld (or in a Vivarium). To check for the star, just look at them until they’re highlighted.
How to catch shiny beasts (farming method)
Beasts have a random chance of being shiny when clearing out dens where they live, or be being bred. The capture method is the fastest, as you can farm for them indefinitely.
Cast Revelio and enter the den with Disillusionment. Hold the left trigger to aim at each beast highlighted by Revelio, and check for a star above their name. If none are shiny, you can catch them all (and sell them for cash in Hogsmeade), or leave the area. Travel back to the nearest fast travel point and rest. This will reset the den and allow you to farm for more shiny beasts.
If you want a “full set” of shiny beasts, you can go for all 11 of them (22 if you count both genders for each beast). The 12th beast, the Phoenix, cannot be shiny and cannot be bred.
Do shiny beasts do anything special?
As far as we can tell with myriad tests involved over the course of a 60 hour save file: no.
Shiny beasts don’t yield any extra items when harvesting them, and they don’t do anything else that’s unique. There are also no achievements/trophies or in-game challenges linked to them. Their appearance and the star next to their name is the only real signifier that they’re shiny.