You can only use 1 "Thunder Dragonmatrix" effect per turn, and only once that turn
The Secret Packs are available in the store until March 28th, but if you are interested in the alternate art cards, it may be wiser to consider the earlier date as the limit
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
If it's not paid, the permanent with cumulative upkeep is sacrificed
A lot of Naya cEDH decks close out games with Birthing Pod lines, and this can be a great way to get a 3-drop for the combo and some other creature you need, which can offer protection from spot removal
Narrative scenarios should scale to three to five boxes