I need to slip Tundra Wolves into the same deck, since it is one of the first cards I played with yet hardly a powerful play compared to other cards that this quiet dual land enables
Create a 2/2 green Bird creature token with "Whenever a land you control enters, this token gets +1/+0 until end of turn." Flashback (You may cast this card from your graveyard for its flashback cost
A mana value of 7 is brutal, but this card greatly ramps up your card advantage and has a place in slower formats like Commander
The red one, [[Cori Mountain Monastery]], is the next best one, I think
If The First Sliver's own cascade ability lets you cast another Sliver card, that Sliver won't have cascade
It isn't enough to completely write this deck off, as there are plenty of very valuable cards that are worth using, but it's worth considering