Balduvian Trading Post

Part of the Alliances cycle of sacrifice lands, each of which enters only by feeding an untapped source of a matching color into the cost: you give up a Mountain already in play (any untapped permanent with the Mountain subtype, basic or dual) to put down a land with utility stapled on. The arithmetic is brutal by design. You pay a card and a turn of tempo (the sacrificed Mountain was producing mana the moment before) to upgrade it into a source that taps for one colorless and one red together, and that can ping attackers for one. The cycle as a whole was Wizards working out how much a land's text is worth: the sacrifice requirement sets the price, the repeatable damage mode is the return, and the whole balance lives in whether that one-damage tax ever earns back the mana you surrendered to put it down. The pinging mode is narrow on purpose, restricted to attacking creatures only, which makes it a defensive tax rather than a removal engine: it shaves x/1 attackers and discourages alpha strikes without ever threatening to clear a board. This is an artifact of a design era when colorless utility lands were priced steeply, before fixing and free entry became the baseline expectation. The whole package reflects how cautiously land slots were treated when every point of incidental damage felt like it needed a meaningful cost attached.