Elderscale Wurm
Most damage-mitigation effects buy time; this one installs a hard floor and then dares the table to find a way over it. Once you sit at seven or more life, no single hit, no swarm of attackers, no burn spell can push you below seven: damage that would do so stops there instead. The threshold is doing two jobs at once. The enters trigger pulls you up to seven if you were below it, so the card can't fail to switch on, and the ongoing replacement effect means a green deck that holds the line at seven becomes nearly impossible to burn out or alpha-strike to death. What makes it more than a fog on a stick is that the replacement is permanent and color-shifted: green almost never gets to ignore damage totals, and asking opponents to find life loss, infect, mill, or some other non-damage clock to break the lock is a real ask in many shells. The body is a clean trampler that ends games on its own, so the protection isn't a tax you pay to do nothing else. The obvious wrinkle is symmetry of timing: the floor cares about your current life, not the source, so it folds against effects that reduce life directly rather than dealing damage. Read it as a green analogue to the white "you can't lose / damage prevention" school, reached through a static life-total rule rather than a prevention shield.
