Good at any point in the game, Fauna Shaman is particularly useful for trading out small creatures you draw during your later turns for larger powerhouses
Beyond these, there are many cards in the deck that generate token creatures, as well as many cards that give +X/+X bonuses to them, allowing you to amass a pretty big army quickly and ensuring you have enough defence to fend off your opponents when it's not your turn
Crop Rotation, Elvish Reclaimer, and Knight of the Reliquary all help find your lands reliably, and the addition of Minsc & Boo, Timeless Heroes provides a secondary win condition
This is the ultimate Commander utility land
They might also run spot removal in the form of [c]Swords to Plowshares[/c], mass removal in the form of [c]Wrath of God[/c], or both
This card is sure to be in consideration for mono-red aggro decks moving forward, thanks to its versatility in low two-mana cost