Darkheart Sliver

Creature — Sliver

All Slivers have "Sacrifice this permanent: You gain 3 life."

2/2

2007-02-01:
The player who controlled the Sliver that’s sacrificed gains the life, not the controller of Darkheart Sliver.
2013-07-01:
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.
2013-07-01:
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.