It means that it is a shiny Pokémon.
It’s a Shiny… if you look him in detail he is brown, the normal one is much darker.
Nice work, you have a shiny Mawile!
It’s a shiny! Congratulations! I am so afraid I am not going to be able to tell Pikachu is shiny and miss it! I did get a Duskull though! It was easy to recognize.