Enchantment - Aura Enchant creature (Target a creature as you play this. This card comes into play attached to that creature.) Whenever enchanted creature deals damage, you gain that much life.1
You only gain life for damage which is not prevented regardless of what the creature damages (player or another creature) or the toughness of the blocking creature. If you put Spirit Link on a Shivan Dragon and it is blocked by a Scryb Sprites, you still gain 5 life points. If the Sprite has Protection from Red, you gain zero life since the protection reduces the damage to zero. [bethmo 1994/07/08]
If a creature has more than one Spirit Link on it, they all work. [Aahz 1994/07/15]
Works for damage due to combat or due to any special ability of the creature. For example, you would get one life for tapping a Prodigal Sorcerer to do damage. [Duelist Magazine #2, Page 9] Note that this is great for creatures which damage you, such as not paying the Force of Nature's upkeep, since you will get as much life as you take in damage.
Damage that is redirected is not considered successfully dealt to the original creature or player, but it may be successful in damaging the new creature or player. [D'Angelo 1998/02/03]
You only gain the life when the triggered ability resolves. If you are reduced to zero life before the ability resolves, you will lose before gaining the life. For example, if the creature with Spirit Link on it attacks you dealing 3 damage when you have just 3 life, you will take 3 damage and lose before the triggered ability can resolve. [D'Angelo 2003/05/16]