1 foil promo card (Mewtwo ex, Nidoking ex, or Persian ex)
In addition to that Johnny-tastic comboing, Pygmy Giant plays well with a lot of fun cards out there
You then get to put any number of creatures from your hand onto the battlefield
Everyone is changing how they track their collection with Dex
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
Sure, one could argue that this dynamic also exists within the physical Pokemon TCG, but at least theres the barrier of having to go to a store and manually open packs, and there arent over a dozen currencies to manage either