Slint, One Without the Swarm

All slivers you control are all colors at all times, and gain, "At the beginning of your upkeep sacrifice this creature unless you return it to its owners hand. If this card is returned to your hand, Search your library for a sliver card and exile it, you may cast that card as long as it remains exiled."
"They had started as a docile, harmless race, which quickly mutated into beings of pure rage and malice."