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Black is actually pretty good at using artifacts, and Marionette Master is a hell of a finisher
This makes using trackers, such as coins or dice , very important
I think that if you wanted to have a discard spell in the sideboard you would probably just want to be playing seven in the main deck, but if you did choose to put one in the sideboard it should be a Duress
Esper Esper, then, is an ally of Grixis, and must have some overlap to keep things balanced