Since the Second Generation, all Pokemon have what are known as
Shiny Forms. Shiny Pokemon are Pokemon that are of a different color than normally found, being extremely rare to find in the Wild. However, Shiny Pokemon are no stronger than a regular Pokemon. Every Pokemon has a Shiny Form, but not all Pokemon can legitimately be found as a Shiny Pokemon.
In Pokemon Sword & Shield, Shiny Pokemon will also be identified when sent into battle with either a Star Sparkle or a (much rarer) Square Sparkle.
Furthermore, if you
Encounter a
Strong Pokemon without owning enough Gym Badges to properly defeat them in battle, these Pokemon will be restricted from being
Shiny at that given time. The
Starter Pokemon also cannot be Shiny when chosen at the beginning of the game (but can be bred in their Shiny Forms via the Pokemon
Daycare), neither can the
Gift Pokemon Type: Null and the
Gigantamax Pikachu &
Eevee Gift Pokemon. Shiny Pokemon will also not appear as Shiny in the
Overworld, making it impossible to know if it is a Shiny Pokemon unless encountered.