Historical Rules · 1 May 2013
Rule 702.13c
Official source text from the 1 May 2013 Rules release
A creature with landwalk is unblockable as long as the defending player controls at least one land with the specified subtype (as in "islandwalk"), with the specified supertype (as in "legendary landwalk"), without the specified supertype (as in "nonbasic landwalk"), or with both the specified supertype and the specified subtype (as in "snow swampwalk"). (See rule 509, "Declare Blockers Step.")