"When a sliver of this breed enters the hive, the others claw each other in frenzied fits, thereby ensuring their rapid growth."
—Rukarumel, field journal

Fungus Sliver

All Sliver creatures have "Whenever this creature is dealt damage, put a +1/+1 counter on it." (It must survive the damage to get the counter.)

Time Spiral Remastered

Premium Deck Series: Slivers

All Sliver creatures have "Whenever this creature is dealt damage, put a +1/+1 counter on it."

Time Spiral

All Slivers have "Whenever this creature is dealt damage, put a +1/+1 counter on it." (The damage is dealt before the counter is put on.)

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.

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.

If multiple sources deal damage to a Sliver at the same time and that Sliver survives the damage, it gets only one +1/+1 counter despite its impressive efforts.