Urborg

Named after the swamp-continent of Dominaria, this is the prototype for the "named basic" design: a legendary land that taps for one color of mana and carries a small piece of rules text aimed at policing a specific interaction. The interaction here is swampwalk, which in the Legends era was a real concern (a meaningful slice of black creatures carried it, and the format had no shortage of mono-swamp opponents to walk past). Stripping swampwalk for a turn at instant speed, off a land that was already in your manabase, is a clean answer to a mechanic the design team apparently expected to see across the table often. The first-strike clause is the stranger half: a black-producing land that can briefly disarm a white or red blocker's combat advantage. What balances both abilities is the tension between the land's two tap modes: using it to police a creature means forfeiting the black mana it could have made that turn, so every combat trick costs you a land's worth of mana that turn. The legendary supertype keeps the rate honest, since the rule of the era meant a second copy in play killed both. The card's lineage runs through Urborg, Tomb of Yawgmoth, which kept the name and the swamp identity but discarded the combat-trick text entirely in favor of turning every land in play into a Swamp. That later printing is the famous one; this one is the design sketch it was drawn from.