When it comes to blue-related creature types, few are as iconic as Merfolk
When you turn Boltbender face up, you can redirect any number of spells and abilities to new targets
Being able to deal with Tarmogoyf for one mana (the previous best answer was Liliana of the Veils second ability or a Ulcerate) was a revolution for the modern format
They weren't as prevelant as cards from previous cycles, but Witherbloom Command has shown up in competitive settings, and Prismari Command does a fine impression of Kolaghan's Command
Bigger creatures even cooler
While this means the opponent will see it coming and not play out additional three-drops, it also means that on the turn your sweeper resolves, youll have mana up to deal with the next threat they play, or the four-drop that they deployed on the turn you played out your Sphere