Catch/Release Spell

Catch:

You hold up a small marble, and attempt to capture a spell for later study as it is cast by another creature.

If the creature is Casting a Spell of 3rd level or lower, it is interrupted and has no effect. Furthermore, the spell is "caught," appearing to be sucked into and suspended in the marble. A spell caught in this form may be copied into your spellbook as if from a Book, but takes twice as long to do so.

If the creature is Casting a Spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 15+ the spell's level. On a success, the spell is interrupted and caught. On a failure by 5 or less the spell is interrupted and has no effect, but the marble shatters. On a failure of 6 or more, the marble detonates in your hand dealing 1d6 force damage per level of of the spell in a 5 foot radius.

Marbles with "caught" spells begin to shake violently after 1d4 days, then detonate as described above.

Release:

If a captured spell is already Known by you, it may be released on your turn as an action. The spell is cast at its originally attempted level, but does not require material components or spell slots.

At Higher Levels:

 When you cast this spell using a spell slot of 5th level or higher, the interrupted spell has no affect and is caught if it is lower than the spell slot you used.