Hydra's Growth

Doubling is the most dangerous verb in counter design because it turns a linear investment into an exponential one, and this Aura hands that verb to green with no ceiling. A single +1/+1 counter arrives when it enters, then every upkeep the total doubles: one, two, four, eight, sixteen. The math outruns the board within two or three turns, and the reason it can afford to is the reason every Aura pays the same tax. The value is welded to a single creature, so removing that creature answers the enchantment and the growth in one exchange. The upkeep clause is the design's release valve: the first doubling waits until your next turn, so the opponent gets a full rotation to respond before the number gets frightening, and the entry counter you do land on cast is small enough to keep that window fair. The card also rewards a running start. Cast it on a creature already carrying counters (from a Hydra's own X, from proliferate, from another counter source) and the doubling begins from a much larger base, compounding what you built rather than starting from one. It is a snowball engine with a single point of failure, the archetypal green trade of raw exponential upside against the fragility of putting all of it on one body.