Nonbasic lands are Mountains.
9/29/2017 If a nonbasic land has an ability that causes it to enter the battlefield tapped, it lose will that ability before it applies. The same is also true of any other abilities that modify how a land enters the battlefield or apply “as” a land enters the battlefield, such as the first ability of Cavern of Souls. This is a change from previous rulings.
11/17/2017 Nonbasic lands lose any other land types and abilities they had. They gain the land type Mountain and gain the ability “: Add to your mana pool.”
11/17/2017 Magus of the Moon’s effect doesn’t affect names or supertypes. It won’t turn any land into a basic land or remove the legendary supertype from a legendary land, and the lands won’t be named Mountain.
11/17/2017 If a nonbasic land has an ability that triggers “when” it enters the battlefield, it will lose that ability before it triggers.