Equinox

White had almost no way to interact with spells on the stack in 1994, and this Aura is one of the strangest workarounds the early color pie produced. Instead of handing white a counterspell (which the color was not permitted to have), it makes the manabase self-defending: enchant a land, and tapping that land counters anything that would destroy a land you control. The threats it answered were the format-warpers of the era (Sinkhole, Stone Rain, Ice Storm, Armageddon), and white had no native response to any of them. Note the elegance of where the cost lives. You pay one white up front and attach to a single land, but the protection radiates outward to your whole board, gated only by the enchanted permanent's tap. The counter is free at the point of use, paid by the very resource being attacked. It is also a clean early example of a principle white's hate cards still follow: a narrow answer can be priced aggressively because it does nothing against most decks, so it can afford to be devastating against the few it targets. Its obscurity now is downstream of the threats it answers having largely been priced out of competitive play, but the template (cheap, narrow, lands-matter interaction in a color that otherwise cannot touch the stack) keeps recurring.