Essence Sliver

Oracle Text

Whenever a Sliver deals damage, its controller gains that much life.

Card Rulings

10/4/2004 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.
7/1/2013 Abilities that Slivers grant, as well as power/toughness boosts, are cumulative. However, for some abilities, like flying, having more than one instance of the ability doesn’t provide any additional benefit.
7/1/2013 If the creature type of a Sliver changes so it’s no longer a Sliver, it will no longer be affected by its own ability. Its ability will continue to affect other Sliver creatures.