If played early into a game, a Hedron Crab can mill substantial sums of cards for the minimal investment of one mana
Mahadi, Emporium Master Mahadi, Emporium Master benefits from a build with creatures that sacrifice themselves in some way
Vigilance , Discard Sunblade Samurai: Search your library for a basic Plains card, reveal it, put it into your hand, then shuffle
But there is another type of crystal worth mentioning, which is also important in the context of Magic: The Gathering
Additional land plays come in many forms, from needing to deal combat damage with Sword of Forge and Frontier, to the simple green enchantment Exploration, and the mana fixing Dryad of the Ilysian Grove
Ragost, Deft Gastronaut This lobster rocks