Warping Wurm

Phasing as an upkeep tax, inverted into a growth engine. Most of Mirage's phasing cards used the mechanic as a defensive trick or a way to dodge sorcery-speed removal; this one taxes you for the privilege of keeping a 1/1 in play at all, then rewards the surrender. The design tension lives entirely in the upkeep choice, and the Phasing keyword sets the rhythm: a creature that is phased in will phase out automatically during your next untap step no matter what you paid, so the body can be present every other turn at most. Pay on an upkeep where it has phased in and you keep it for the turn; decline the payment and it leaves on its own, surviving everything (it is not a legal target, not subject to board wipes, not anything at all) until it phases back in on a later turn and collects a +1/+1 counter. The free play is the loop itself: letting it go costs nothing and grows the body, while the four-mana toll is the price of ending the loop and leaving the wurm on the battlefield to attack. Because no one receives priority during the untap step, the phase-in trigger is delayed and lands on the stack alongside the upkeep tax, so you decide the counter and the payment in the same window. A genuinely strange card from an era still figuring out what phasing was for, and one of the few that made the mechanic the point rather than a footnote.