Piggybacking on this same train of thought: If I have a basic
Island and I activate a
Navigator's Compass to grant it the swamp land type, would
Cabal Stronghold count the basic Island that has gained the swamp land type as a basic swamp?
Is the answer the same for that basic Island if I have an
Urborg, Tomb of Yawgmoth in play?
Basic: Its type line specifies Basic, and neither Navigator's Compass nor Urborg, Tomb of Yawgmoth changes this.
Quote:
205.1b Some effects change an object’s card type, supertype, or subtype but specify that the object
retains a prior card type, supertype, or subtype. In such cases, all the object’s prior card types,
supertypes, and subtypes are retained. This rule applies to effects that use the phrase “in
addition to its types” or that state that something is “still a [type, supertype, or subtype].” Some
effects state that an object becomes an “artifact creature”; these effects also allow the object to
retain all of its prior card types and subtypes.
205.4b An object’s supertype is independent of its card type and subtype, even though some
supertypes are closely identified with specific card types. Changing an object’s card types or
subtypes won’t change its supertypes. Changing an object’s supertypes won’t change its card
types or subtypes. When an object gains or loses a supertype, it retains any other supertypes it
had.
Example: An ability reads, “All lands are 1/1 creatures that are still lands.” If any of
the affected lands were legendary, they are still legendary.
Swamp: Navigator's Compass with Swamp chosen or Urborg, Tomb of Yawgmoth explicitly adds that subtype.
It's basic and it's a swamp, and that's all it takes to be considered a basic swamp.