This is an amazing house in multiplayer, and Ive written pages on it
So, if you dont have many spells to cast in the early turns of the game or you have just a few lands in play and are trying to keep pace with your opponent foretell will give you something to do with your mana
On the other hand, if you want to lean harder into mana ramp, Jolene, the Plunder Queen is your gal
Vorinclex, Monstrous Raider Vorinclex, Monstrous Raider is a giant monstrous Doubling Season-style card
The archetype that Sliver Swarm focuses on entirely is Combat: the deck provides tons of cards that greatly increase its effectiveness in combat, from dishing out extra damage with Bonescythe Sliver to providing evasion with Cloudshredder Sliver to drawing card on combat with Synapse Sliver
In this case, the ability to return a creature card from your graveyard to the battlefield is the reason why an echo cost is needed on such an under-statted creature