Card Sleeve of Power
From D&D Wiki
These card sleeves were created by Ra'anul Everhate to enhance the powers of his cards. The most basic version is Card Sleeve of (insert Stat Here). These increase the stat named, giving the card master using it double the normal bonus for the stat listed.
The second most common are " Trifold Sleeves". These add to three of the stats, dependant on the color of the sleeves backing as follows.
Red: Dexterity, Intelligence, and Hit Points. Blue: Strength, Constitution, and Saving Throws Silver: Constitution, Dexterity, and Armor Class Black: Armor Class, Hit Points, and Attack Rolls
The third and most powerful are called " Card Sleeves Of Power. These are the ultimate achievement of Ra'anul, they triple the bonuses given by the card inserted.
He made these sleeves to be able to switch between cards, but apon his ascention he changed the fabric of magic to make them bind to the first card they are put on for each owner. This means that once a Card Master uses a sleeve on one of his cards, he can not take it off one to use on another.