Brain in a Jar

The whole engine runs on a counting trick: each activation adds a charge counter and lets you cast an instant or sorcery whose mana value exactly matches the new count, free. That exactness is the constraint, and it dictates everything about how you build around the artifact. A pile of unrelated spells does nothing; you need a curve that maps cleanly onto the counter sequence, so that turn after turn there is always a spell costing exactly the number of counters sitting on the jar. The reward for solving that puzzle is steep, because the cast is mana-cost-bypassing and stacks up fast. A jar that started at one and climbs leaves you firing off increasingly expensive spells for a single mana per turn, and the gap between a spell's printed cost and what you actually paid widens with every counter. The scry mode is the relief valve: when the matching spell is not in hand, you cash counters in to dig for it rather than wasting an activation. It is a build-around in the truest sense, the kind of artifact that is unplayable in a deck assembled by raw power level and lethal in one assembled by mana value, where the counting is the deckbuilding. The friction lives entirely in that "equal to" clause; everything interesting the card can do is downstream of having to hit the number on the nose.