Software developers deploy changes fought with unanticipated consequences. To their benefit we enhance system observability with temporary changes we call spells. We apply and remove spells quickly. The rapid feedback builds more reliable intuition with respect to systems that can never be completely understood.
In fiction the use of magic frequently manifests itself in a transformation of a character, if not the transformation of the fictional world. wikipedia 
Spells have some similarity to feature flags but don't often apply to individual features.
Game days and chaos monkey build confidence that our systems can survive abuse and that we can diagnose their failures when they don't. Spells accelerate this learning cycle based on having reliable diagnosis infrastructure already in place.
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We offer two broad spells in an early recreation of our network simulator. open