LifeLink is an activated ability that heals a planewalker each time the creature with the ability damages another unit. LifeLink heals the planeswalker for the exact damage done by the creature with the LifeLink ability.
Bobby attacks his opponents' Iron Grappler with his Child of Night. Since Child of Night has LifeLink, Bobby's planeswalker will be healed for 20 health, the amount of damage his Child of Night deals to the opponent. On the next turn Bobby's Opponent responds by ordering his Iron Grappler to attack Bobby's Child of Night. The Iron Grappler deals 30 damage to the Child of Night and kills it. Becuase the Child of Night did no damage, Bobby does not recieve any health from the combat.
Notable Cards that use LifeLinkEdit
MTG: TCG Player's AnaylsisEdit
There is no significant difference in how LifeLink works in Magic the Gather: Tactics and the paper card game.