Ok. So it's pretty clear to me that, based on various comments, magical grapples are pretty much broken. However, storyline wise, they make sense to exist. So, I came up with several rules to have magical grapples be less crappy, gameplay wise:
1. Before a magical grapple can be initiated, a target must have a taggable/invokable aspect relevant to grappling (and obviously, the aspect must be tagged/invoked).
2. Once the aspect has been tagged or invoked, the spell may be cast. The strength of the spell = the strength of the grapple. Take a mental stress to cast the spell, and roll Discipline to control. HOWEVER, any shift of failure in the spell casting MUST be directed to fallout, affecting the strength of the grapple.
3. The default duration of the grapple is one action: you may affect the original strength of the grapple to extend to duration (as per normal rules), or you may use a supplemental action and take one mental stress to extend the grapple (using Conviction + specializations/foci to determine the number of exchanges the grapple has increased by, and assuming a roll of zero on Discipline + Specializations/Foci against the extension to determine fallout).
4. Every exchange, you must take an action to roll Discipline + Specializations against the original number of shifts of power you have applied to the grapple. Any failure must be taken as fallout against the grapple strength. THIS DOES NOT AFFECT THE NEXT STRENGTH YOU MUST BEAT NEXT TIME TO NOT TAKE FALLOUT.