User blog comment:K'eth, Undercover Agent/Testing Ground 4: A Shrine to All of Your Mockeries./@comment-25985177-20160531231057/@comment-25985177-20160601120516

A planeswalker can only channel mana from other planes other than their plane of origin if their spark has been ignited. Which means he would have to planeswalk. BTW most eldrazi are dead now so theres that.