Rock Hydra

Every later X-cost hydra has either honored or rejected this card's design template, and the architecture is unusually intricate for an Alpha printing: enter-the-battlefield counters that double as a damage-prevention shield, a red mana sink to pre-empt small pings, and an upkeep-only regrowth clause that asks you to invest mana over multiple turns rather than spend it all on the cast. That last restriction carries the balance. Without the upkeep limitation, a resolved hydra with mana behind it would simply outscale every burn spell in the format; with it, the card forces a tempo choice between developing the board and rebuilding the threat, and gives the opponent a window to finish it off before the counters come back.

What dates the design (charmingly) is the per-point damage prevention. Modern hydras treat +1/+1 counters as raw stats and die to lethal damage like anything else; this one treats each counter as a literal head, removed one at a time, and reads as a creature whose toughness regenerates head-by-head rather than a creature with a toughness number. That literalism explains why the card has stayed a flavor touchstone even as its rate has been eclipsed: it is the rare early-Magic creature whose rules text is doing the work of the art rather than the other way around.