Ruins of Oran-Rief

Built to subsidize a single, narrow archetype: colorless creatures, which in practice means Eldrazi. The mana ability is boilerplate utility-land tax (enters tapped, produces one colorless), but the second ability is the reason the card exists, growing a colorless creature that entered the same turn. That timing clause is the whole constraint. It cannot buff a body already on the board; the reward only lands on something fresh, which converts the land into a recurring incentive for a deck that keeps flooding new Eldrazi onto the table rather than a generic combat trick stapled to a land. The payoff scales with how many colorless bodies you can chain out turn after turn, so the card wants a board that is constantly refilling. The cost of that focus is total: outside an Eldrazi-leaning shell the activated ability is dead text, and you are left with a tapland producing colorless mana, which most decks would rather not run. This is a tribal payoff hidden inside a land slot, free support if you are already committed and worthless if you are not.