The directors of the Riptide Project wanted instant results on the sliver experiments. They got their wish.

Quick Sliver

Flash
Any player may cast Sliver spells as though they had flash.

Commander Masters

Secret Lair Drop

Premium Deck Series: Slivers

Flash
Any player may cast Sliver cards as though they had flash.

Salvat 2005

The first ability applies when this card is not on the battlefield. The second ability applies when this card is on the battlefield.

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.