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
Dragonstorm Globe
7 Purphoros, God Of The Forge Get Those ETBs The Gods of Theros are pretty darn strong, and Purphoros, God of the Forge is one of the more impressive ones
and Toski, Bearer of Secrets
That's not to say there aren't issues, though, and I definitely think there's a number of ways that this can be improved upon
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