All lands lose all abilities except mana abilities.
A mana ability is an ability that produces mana, not an ability that costs mana.
Land cards not on the battlefield aren’t affected.
If a land has an ability that triggers “when” it enters the battlefield, it will lose that ability before it triggers.
If a land has an ability that causes it to enter the battlefield tapped, it will lose that ability before it applies. The same is also true of any other abilities of a land that modify how it enters the battlefield or apply “as” it enters the battlefield, such as the first ability of Unclaimed Territory.
If a land gains an ability after Blood Sun has entered the battlefield, it keeps that ability.
If a land has an ability that continuously changes the types of other lands (such as Urborg, Tomb of Yawgmoth does), that ability will apply before Blood Sun removes that land’s abilities. If a land has an ability that grants abilities to other objects, Blood Sun will stop it from doing so.
