Because of their powerful effects, some Trainer cards limit the player to only playing one of the same type of card, such as a supporter, per turn
Aristocrat decks are largely in the other color combinations, but by going into blue and black, this means theres new space to explore
Spellslinger decks already want to leverage cards like Firebrand Archer and Guttersnipe as damage sources, so it takes almost no deckbuilding concessions to make this a nasty card draw engine
Blue Mana Control and Knowledge Blue mana, sourced from islands, represents intellect, manipulation, and the pursuit of knowledge
You can toss four of these into a deck and then reliably draw one and drop it on turn four
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