Elvish Vatkeeper

Most cards that seed an Incubator leave the payoff at a flat : pay it, flip the token, get a body sized to the counters it was born with. The extra lever here is a activation that transforms a target Incubator token you control while doubling its +1/+1 counters, converting the flip itself into a multiplication step. The default incubate 2 makes a token that would flip into a 2/2; run it through this ability and you transform it into a 4/4 instead, and if you can pile more counters onto Incubators from elsewhere, the ceiling climbs quickly. The cost structure is the honest constraint: is steep, and the ability is single-use per token. Once an Incubator transforms, its back face is a Phyrexian artifact creature that no longer carries the Incubator subtype, so it can never be targeted again; each token gets exactly one inflation. That pushes the card toward width rather than a single runaway threat, rewarding a board where you seed several Incubators and mana outpaces what you have to spend. As a 3/3 for its cost that leaves a growing artifact-creature-in-waiting behind, it sits in the black-green counters tradition without leaning on the graveyard or a sacrifice outlet; the value lives entirely in the incubator queue and the mana to unlock it. The enter trigger fills the queue, the activated ability inflates it, and the payoff arrives larger than the mana ever suggested.