For Gruul mana-fixing, I recommend prioritizing dual lands that count as both Forests and Mountains: Cinder Glade, Stomping Ground, Sheltered Thicket, and Taiga (if you're willing to spend lots of money) add layers of extra synergy to the deck because they can be fetched by lands (Wooded Foothills) and spells (Wood Elves) while also empowering cards that care about land types like Valakut, the Molten Pinnacle and Howl of the Night Pack
Similar to Birthing Pod from the past, you can use it to enable a combo, but it can also just act as a card advantage engine and/or influence the board state via the -1/-1 counters
Even though it has since been reprinted in Commander Legends, the original white-bordered P3K version remains the ultimate flex
Read More: MTG Secret Lair Manager Teases Big Changes in the Future
Doubling the mana produced by your islands enables some incredible turns, especially with effects like Turnabout and Time Spiral