Jihad
Notorious less for its design than for its name: the card was functionally retired by Wizards in the mid-1990s, with the name treated as unprintable in any future reference. The mechanic itself is a fascinating early experiment in conditional anthems, predating the modern vocabulary for hate cards and pump effects. The triple-white cost gates it to mono-white aggressive shells, and the design ties a substantial combat boost (+2/+1 across the team) to an opponent's board state, with a self-sacrificing failsafe when the chosen color disappears. That structure (you name a color and an opponent at resolution, then ride the anthem until your opponent controls no nontoken permanents of the named color) is the ancestor of every "as this enters, choose" hate enchantment that followed: the Circle of Protection cycle had already explored choose-a-color, but binding the choice to a specific opponent and using their board as the on/off switch was novel. The flavor framing, an anti-infidel crusade aimed at a named enemy, is what made it untouchable. Wizards has reprinted nearly every other Arabian Nights card of consequence in some form; this one sits in a small category of designs the company has deliberately walked away from. The mechanical chassis is reusable and has been reused, with new names attached; the original remains a collector's artifact and a case study in how flavor decisions, not power level, can end a card's life.
