Vadrik, Astral Archmage

Most cost reducers cap out at a fixed number; this one couples its discount to a stat that the day-night mechanic exists to grow. The reduction starts at one mana off (Vadrik's printed 1 power) and climbs by one every time the day-night dial flips, since each flip drops a +1/+1 counter on him. That coupling is the entire engine. On its own the 1/2 body offers a generous but bounded discount to instants and sorceries; add cards that swing day into night and back on demand and the power creeps upward, which in turn cheapens the very spells that let you keep swinging the axis. The result is a self-referential loop where each cycle hands you a slightly cheaper turn, and eventually your spells resolve for close to nothing. The design's honesty lives in its fragility: the reduction is only ever as large as Vadrik's current power, and there is no floor beyond the printed one mana off, so a single removal spell zeroes out the accumulated counters and resets the whole slope. He also reduces instants and sorceries only, never permanents or abilities, which keeps the payoff narrow enough to build toward rather than splash into anything. The interesting part is the growth curve itself: a value slope that treats the day-night axis as a resource to be pumped, not as flavor text to be observed.