Quirion Dryad

Green almost never wants to cast white, blue, black, or red spells, which is exactly the constraint this design leans on: it turns a green body into the payoff for a deck that is mostly other colors. The growth condition deliberately excludes green, so it does nothing in a mono-green shell and everything in a spell-dense multicolor one. That made it a cornerstone of the threshold and "miracle grow" archetypes built around cheap cantrips and disruption, where a starting 1/1 could outgrow removal windows in a turn or two as a stack of off-color spells resolved. The counter accrual is permanent and stacks with itself, so it rewards a low curve and a high spell count rather than a single haymaker: a hand of one-mana cantrips and pieces of interaction is worth more to it than one expensive bomb. It also reads as an early experiment in the design line that later produced Tarmogoyf and Kiln Fiend: a small green creature whose size is a ledger of what the rest of your deck has been doing. The wrinkle is that it grows on cast, not on resolution, so even a spell that gets countered still feeds it, which quietly encourages jamming threats into open mana and casting into a held counterspell without fear of losing the growth. A 1/1 whose size scales with how little green your deck actually runs.