Delay Magic

You attempt to delay a creature in the process of casting a spell by freezing the Weave around them in time. When you cast this spell, roll a d4.  The target creature's magic is delayed by that many turns.  During those turns, it may still try to cast spells as it wishes, but they will have no effect.  At the end of the duration, all spells cast during the duration occur simultaneously.  If the spell has a target, and the target is still within range, the spell is cast as intended.  If the spell has a target, but the target is out of range, the spell fizzles, and the spell slot used to cast it is used.  If the spell has multiple targets, it still effects all original targets that are still in range. If the spell targets a specific area rather than an individual, it will occur in the designated area if that area is still in range.  If the area is no longer in range, the spell fizzles and the spell slot used to cast it is used. If the spell extends from a certain part of the person and doesn't have a target, it goes out in whatever direction that part of the caster is pointing at.  The delay ends at the beginning of the turn number that was rolled. 

The force of the arcane energy leaves the castor lethargic: until their next turn, they may only take an action or bonus action, they cannot take a reaction, and their speed is halved.

The caster is aware that their magic has been delayed, but is unaware for how long.