Kang the Conqueror

The extra-turn effect has always been the most carefully rationed spell in blue, and the design here is a study in how to hand one out on a permanent without letting it spiral. The power-up buys an additional turn, but it fires exactly once, it grows Kang by a single counter, and it explicitly locks out every power-up ability during the turn it grants: no chaining a second extra turn out of the first, no assembling a stack of counters in one loop. The price is the other governor, eight mana steep enough that the turn you take had better already have a board behind it. What the ability rewards is not a combo trigger but a tempo already in your favor: a 4/5 flier that turns your best turn into two of them, then walks away as a bigger body with the button spent. The cost-reduction clause tightens the timing, subtracting his own mana cost () from the activation if he arrived that turn, which leaves a bare to pay: still one blue pip, but light enough colored requirement that a same-turn extra turn becomes reachable when the rest of your hand is empty enough to want one. It sits in the lineage of Time Walk and the blue extra-turn spells that followed, but where those are one-shot cards you cast and forget, this keeps the effect on the battlefield under a one-per-copy leash, trading repeatability for a single, expensive, decisive swing.