He encourages you to build your deck with a lot of mana value 3 or less creatures, and gives you a mini-Winota style effect
That's because one (with art by Andreas Rocha depicting a waterfall of lava dumping into a mountain stream) is from the actual expansion set Dragons of Tarkir, while the other (with art by Noah Bradley depicting a river of lava winding towards an oasis) is one of the possible prizes from the Dragonfury Promo, a dexterity-based dice throwing game available at select Dragons of Tarkir prerelease events
With a ward effect with a cost of two life, you can be sure your opponents will always be paying life, whether it be through combat or that ward effect
While other filterlands are scattered throughout the Final Fantasy decks, these two are by far the most expensive, simply because they've not seen many reprints
These colors do work well with instants and sorceries, in-line with Gandalf's spellcasting theme, but it would've been better in white mana with related effects to please dedicated LotR fans cracking Tales of Middle-earth Boosters