Deekah, Fractal Theorist

Most magecraft payoffs treat every spell as interchangeable fuel: a Young Pyromancer token, a Storm count, a fixed trigger that fires the same whether you cast a cantrip or a game-ender. This one scales its reward to the cost of the spell that caused it. The Fractal it makes arrives as a 0/0 and immediately takes counters equal to the triggering spell's mana value, so cheap spells build a wide board of small bodies while a single expensive instant or sorcery produces a genuine threat in one trigger. The design ties the payoff directly to how top-heavy your spellbook is, which is an unusual axis: it rewards the exact thing most spellslinger shells are built to avoid, namely casting high-mana-value spells. The unblockable activation is the finisher grafted onto the magecraft engine, converting one oversized Fractal into a clock that connects. It reads as a build-around because it is one: the counter magnitude means the difference between a swarm and a haymaker depends entirely on what you're willing to cast, and the second ability exists to make sure the biggest of those counters actually matters in combat rather than sitting on a token the opponent can chump forever.