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This is not related to game play as far as I know. Creatures such as Shivan Dragon, Victory's Herald and Glyph Keeper, and even enchantments like the double-sided Search for Azcanta, there is this shiny part near the bottom of the card. The only link that I have is that it is linked to rarity, because only cards that are rare and above have them, but not all of the cards that are rare and above do have them, and it is not related to premiums. Can anybody help me know what it is?