6-level Transmutation
Whenever a creature casts a spell within range, the caster may choose to capture that spell as a reaction and add it to their list of spells. Readying the spell can be done in combat, taking up an action and a bonus action to study the spell. Any focus or components to cast the captured spell are still required, casting time is unaffected. Only a successfully cast spell can be captured, and the original captured spell will remain unhindered. Whenever a new spell is captured, it replaces the oldest one and must be studied again.
When you cast this spell using a spell slot of 8 or higher, the caster may capture an additional spell at level 8. At level 9, you gain the ability to combine the affects of the 2 captured spells into a new higher ranked spell (spells can only be combined if the total of their spell levels equal 8 or less, this also determines the level of the combined spell).