Blinkmoth Nexus

Tap it for colorless mana on the turns you need a land, animate it for a single mana on the turns you need a threat, and you have the manland template most others are still measured against. The crucial restriction is the price of becoming a creature: one mana every turn it attacks or blocks, plus the colorless it produces being off-color in a deck that wants flyers. That tax is what keeps an evasive 1/1 from being free, and it is paid only when you choose to commit. The self-pump activation is the wrinkle that makes a board of them lethal: multiple Nexuses can stack +1/+1 on each other, turning a clutch of one-mana attackers into a clock that closes out a stalled game. It dodges sorcery-speed sweepers by sitting dormant as a land until the moment you want it live, and it dodges sorcery-speed removal aimed at the rest of your board because it simply is not a creature until you say so. The Blinkmoth typing on the pump is largely vestigial flavor in practice (almost nothing else cares about being a Blinkmoth), but the structure it set up, a colorless land that turns sideways without spending a card, became the load-bearing piece of a long line of value lands that followed.