The Precon List Before we talk upgrades, let's take a look at the stock list to see what we're working with: Sliver Swarm lives up to its name with a complete focus on Slivers: I count 40 sliver creatures in the deck plus 3 cards that can count as slivers like Titan of Littjara, and then 9 more nonland cards that care about slivers
Overwhelming Stampede is usually used in decks that play a lot of token creatures, but even with, say, a 5/5 Riku, casting two copies of the Stampede will lead to 20 trampling commander damage
Also, make sure to stick to Standard decks when building, because then you dont need to worry about facing off against decks built from older sets, which most often means avoiding double-energy
Slowking was also eventually banned after the set's release for some powerful exploits
What this means in practice is that if youre purely attacking, its much the same as any untap effect