Gelaji, Ouroboros of the Dunes

Prevent all noncombat damage that would be dealt to Gelaji, Ouroboros of the Dunes.
Substantiate —Whenever Gelaji becomes tapped, if it's not attacking, target land an opponent controls becomes a Desert with "{t}: Add {c}" and loses all other types and abilities.
{4}{w}{b}{g}, {t}, Discard a card: Choose up to one target creature. Destroy the rest.