>>361850872/2
Standard Pokemon are everything that you can think of that isn't the other 3 categories. Good examples are Scizor, Bulbasaur, Bidoof, Passimian, you get the gist. Standards can only be traded for standards. Legendaries cover UBs, Box legends, individual Legendaries, and sets of Legendaries. Examples of each would be Naganadel, Lugia, Heatran, and the Regi trio + Regigigas. Legendaries can only be traded for Legendaries. Mythicals are Mew, Celebi, Jirachi, Deoxys, Shaymin, Darkrai, Arceus, Victini, Keldeo, Meloetta, Genesect, Diancie, Hoopa, Volcanion, Magearna, Marshadow, and Zeraora. They won't be able to be requested and this aren't able to be traded through the GTS. Shiny is more of a sub category that stacks onto other categories. Shiny Pokemon can only be traded for other Shiny Pokemon. This rarity system is to ensure that everyone leaves the GTS happy with what they traded, knowing that it was a balanced transaction, and can more easily prevent children or new players from freely letting go of valuable Pokemon.