Battlefield Thaumaturge

Most cost reducers shave a fixed amount or care about a card type; this one keys off targets, and targets are precisely what blue's spell-slinging decks were already counting. The reduction scales with how many creatures a spell points at, which quietly rewires the math on every multi-target effect: a fight spell that hits two creatures, a divided-damage burn spread across a board, a Strive pump that names three of your attackers. Stack enough targets and the reduction can swallow most of a spell's cost, turning a multi-target combat trick into something close to free. The one caveat the math demands: a spell only counts the creatures it actually targets, so a blanket mass-pump that affects your whole team without targeting anything gets no discount at all. The heroic clause is the second half of the design, and it solves the obvious problem with a 2/1 that wants you to aim spells at your own creatures: any of those spells, pointed at this body, hands it hexproof for the turn, so the removal that would normally answer a fragile engine can no longer reach it on your own turn. The two abilities feed each other, since the spells you cast to trigger heroic are often the same multi-target spells the reduction discounts. It is a build-around in the truest sense: dead in a deck of singleton removal, an engine in one stuffed with spells that touch creatures. The fragility is the honest price, since one point of toughness means any incidental damage or a removal spell on an off-turn ends it before the engine ever spins.