While Plainscycling and Islandcycling are abilities of Sanctum Plowbeast, even though you can activate those abilities from outside the battlefield, Sanctum Plowbeast itself is merely an artifact card when it's not on the battlefield, and Grand Architect's restriction on artifacts means it's restricted to permanents with the artifact type and therefore doesn't allow you to spend the mana on abilities of artifact cards.
It's not as simple as providing a single rule quote here, but the entirety of 110.4 will back this answer.
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BlueScope says... Accepted answer #1
You cannot.
While Plainscycling and Islandcycling are abilities of Sanctum Plowbeast, even though you can activate those abilities from outside the battlefield, Sanctum Plowbeast itself is merely an artifact card when it's not on the battlefield, and Grand Architect's restriction on artifacts means it's restricted to permanents with the artifact type and therefore doesn't allow you to spend the mana on abilities of artifact cards.
It's not as simple as providing a single rule quote here, but the entirety of 110.4 will back this answer.
May 29, 2017 3:11 a.m.