Castle Garenbrig

Oct 4, 2019 · Although the common lands have basic land types, they aren't basic lands.

Oct 4, 2019 · The mana generated by Castle Garenbrig's last ability can't be spent to activate abilities of creature cards that aren't on the battlefield.

Oct 4, 2019 · Once the common lands (such as Mystic Sanctuary) enter the battlefield tapped, there's no way to untap them with a spell or ability to make their last ability trigger.