Sunbond

Lifegain on its own is a non-board-state activity: it moves a number that does not threaten anything. This Aura converts that idle resource into a clock, taking the incidental lifegain that usually sits at the margins of a deck and turning it lethal. The conversion is total and immediate: each instance of gaining life puts that many counters on one creature, so a single large drain or a Soul Warden-style payoff dumps a whole stack of life onto one body at once. That makes it a multiplier on lifegain a deck is already producing rather than a payoff that asks you to do anything new. Pairing it with lifelink is the obvious move, though the timing is less explosive than it looks: lifelink damage is simultaneous with regular combat damage, and the counters arrive only when the triggered ability resolves afterward, so the attacker does not grow in time to survive a lethal block or push through extra damage that same combat step. The body is bigger for next turn, not this one. The cost is the one every Aura carries: it commits two cards and four mana to a single creature. Removing Sunbond itself does not undo the counters already placed, since they live on the creature independently; only killing the host takes the Aura with it and drags those counters into the graveyard alongside the body. It reads as a glue piece for lifegain-counters strategies, not a centerpiece.