If you can give your opponent tokens and then kill them with something like Pestilence, you could easily grow your Rat army
But these rules also permit a certain degree of consistency in game planning and play, such that decks are not just a completely random agglomeration of powerful cards, but can actually constitute strategies. The 60 card minimum and 4 card maximum was a brilliant balancing of these elements, replayability and consistency, that has helped Magic endure for decades
The card has to also be desirable outside its artificial scarcity
Two top-tier staples of sliver Commander decks are Morophon, the Boundless as a changeling that heavily discounts multi-colored slivers, and Sliver Hive as an ideal 5-color land for the critters
Sudowoodo (Fighting / Space-Time Smackdown) This goofy tree has a one-energy attack that deals an extra 30 damage to ex Pokemon (which so many people run anyway), making it a very strong opening move
At the time, land theme seemed to just mean ramp with a light graveyard theme enabled by a generic Jund value package