Glyph of Life
Uncapped lifegain off a single white mana sounds like a constructed-format problem until you read the conditions that keep it honest. The spell does nothing without a Wall already on the battlefield to point it at, and because it is an instant that only lasts the turn, the realistic line is to hold it until your opponent has committed attackers into your Wall, then cast it in response: whatever damage those attackers deal to your chosen Wall comes back as life, scaling with however much gets dealt, so a Wall absorbing several attackers returns life for each of them. The Wall-only target is the friction that earns the uncapped gain; without a defensive board built around the right creature type, the card is a blank. In an era when twenty was the whole game, that arithmetic could swing a race. This is the white member of the Glyph cycle from Legends, five one-mana instants (one per color) that each target a Wall and bend combat around it, and the only one that turns the Wall into a lifegain engine rather than modifying its stats or combat math. The whole premise rests on a world Legends genuinely tried to support, where Wall of Swords and Living Wall held the line and dared opponents to crack through. What survives is a fossil from a moment when Wall was a type Wizards thought worth supporting at instant speed, before it dissolved into the broader Defender keyword and took the cycle's reason for existing with it.
