Like most Magic: The Gathering cards, the value of The Darkness Crystal depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Final Fantasy)
Boros decks often have plenty of good keywords, but they are often on singular creatures
If you exiled a nonland card this way, create a Treasure token. More creatures is good, and Treasure tokens are famously absurd, so this seems like a great card in Lost Caverns of Ixalan
Market value: Around USD ~$1,560 in guides
Retrace (You may cast this card from your graveyard by discarding a land card in addition to paying its other costs.) Fires out
If you've been paying attention to the story, it's a huge deal: everything has converged at this one place, at this one time