Rune of Sustenance

Every Rune in the cycle solves the same problem the same way: an Aura that grants a narrow, modest bonus is a bad card unless it stops costing you a card, so each one draws when it enters and downgrades its worst case to a two-mana cantrip with a small buff stapled on. This is the lifelink branch, and like the rest of the cycle it splits its grant across two host types. Enchant a creature and it drains you back on combat damage directly; enchant an Equipment and the lifelink follows whatever creature currently carries the gear. That Equipment mode is the clever one, because it sidesteps the structural weakness of Auras entirely. An Aura normally dies with its host, a one-time attachment whose value evaporates the moment the creature does. Ride it on an Equipment instead and the buff becomes portable, surviving every death and re-equip, a lifegain package that outlives any single body. The payoff on either target stays deliberately small, which is the point: the buff never has to justify a deck slot on its own, because the enters-draw already paid for the attempt. What you are really buying is life off combat you were already going to have, with the card refunding itself so the only real cost is the mana and the click.