Bat Colony

A payoff that turns a land subtype into a resource meter. The token generation scales not with total mana but specifically with mana produced by Caves, which reframes those lands as spell components rather than fixing: every Cave you tap toward this spell is another flying body on entry, so the card rewards a manabase built around a single land type in a way most white enchantments never bother to ask. The second ability closes the loop, converting the ongoing act of playing Caves into a slow +1/+1 counter engine that grows a chosen threat as the game develops. What makes the design cohere is that both halves point at the same axis: front-load your Caves and you get a wide swarm now, drip them in and you get a tall creature later, and a deck committed to the subtype gets both. It is a build-around that hands you nothing generic, an enchantment whose ceiling is entirely a function of how far you were willing to warp your lands to feed it, and whose floor is unusually punishing: cast it without spending a single point of Cave mana and the enters trigger creates zero tokens, leaving a do-nothing enchantment on the battlefield waiting for a Cave to justify it. The counter clause is what keeps that floor from being total, since it keeps producing value long after the entry trigger resolves, giving the card mid- and late-game relevance rather than a one-shot burst.