Lands wins by assembling Dark Depths/Thespian's Stage or just grinding with Life from the Loam while Wasteland denies your mana, so you want to race before they lock down your lands and to protect your own graveyard plan. Silent Gravestone is a cheap artifact that stops Life from the Loam from targeting the land cards in their graveyard, which blunts their grinding engine. Keep in mind it also stops your own targeted graveyard effects like Dread Return and Golgari Thug's trigger, and it does nothing to Dark Depths' ice counters. Unmask lets you take a nonland card like Crop Rotation or Life from the Loam out of their hand before they can use it (it can't take Wasteland or other lands), which is valuable since they have little interaction once you're going. Poxwalkers and extra loot are cut since this matchup rewards speed over grinding card advantage.