This is a reactive kind of deck list, and you should always be updating these slots with answers to the decks currently giving you trouble
Pteramander, Spectral Sailor, and Brineborn Cutthroat do offer some of that Mono-Blue Aggro touch, but for the most part its looking like the usual suspects of cantrips, counterspells, and card advantage are the story of the blue column
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Call to the Kindred seems like the perfect fit for a deck like this provided you can make it around to your next turn with it still enchanting one of your Slivers
Goldspan Dragon will give you the mana to cast bigger and bigger spells each time it attacks, and your opponents will have to pay a price to remove it, too