Dwarven Patrol

The 4/2 body for three mana is the bait; the untap clause is the leash. A creature that skips its own untap step swings exactly once before it freezes, and the only thing that thaws it is casting a nonred spell. That condition keys on color, not card type, so any off-color cast does the work: a blue counterspell, a white removal spell, even a colorless artifact will untap the Dwarf, which means a mono-red deck running a handful of artifacts can feed it without a second color at all. The card is an incentive to diversify, blunt and literal: most multicolor-matters designs of the era handed you a bonus for playing extra colors, while this one withholds the creature's entire ongoing function until you comply. The trigger fires on the cast, not on resolution, so it untaps even if the off-color spell is countered, and it can untap more than once across a turn if you keep casting nonred spells. Note the precise wording: a red instant, sorcery, or enchantment will not free it, since those are red spells. That requirement is also why it never stuck. The decks that wanted a cheap four-power attacker were the ones least willing to dilute their mana, and the two- and three-color decks that could reliably feed it already ran three-drops that asked for no tax to function. A clever piece of conditional design that wanted the one thing its natural home was least inclined to give.