Wood Elemental

Few cards illustrate the early design team's struggle with variable power and toughness as starkly as this one. The sacrifice clause happens as the creature enters, after you have already tapped your lands for the four mana to cast it: now you are asked to sacrifice untapped Forests to give the thing a body, and you have spent most of them. In practice the elemental usually enters as a 0/0 and dies immediately unless you have gone out of your way to flood the board with Forests you have not used this turn (a Fastbond line, a mid-turn ramp burst, an untap effect). What looks like a clever puzzle on paper is, at the table, a trap. Compare the modern green stat-checks: Tarmogoyf, Multani, Maro himself all measure power against a resource you accumulate without spending. This one measures against a resource you have to refuse to spend, a fundamentally harsher contract. It has been errata'd more than once to clarify the timing, but no errata repairs the underlying tension. A historical curiosity, and a useful reference point for why "sacrifice as it enters" largely vanished from the design vocabulary.