Needs review
Source: Complete Book of Eldritch Might

Description: You counter a spell and absorb the energy unleashed to power another spell.

Prerequisites: 3rd Level Caster

Whenever you use the counterspell action and successfully counter a spell, you absorb the energy of your opponent's magic and can use part of it to power a spell at least one level lower than it. The powered spell does not disappear when you cast it, or (if you cast spells like a sorcerer) you do not use the spell slot. You must use the power you have absorbed on the next spell you cast or lose it. For example, if you counter and consume a 4th level Ice Storm, you can cast a 1st, 2nd, or 3rd level spell that you have prepared (or if you do not prepare spells, one that you know) without losing the spell or slot. If the next spell you cast is 4th level or higher, you lose the consumed energy. Consuming a 1st level spell allows you to cast a 0th level spell. Consuming a 0th level spell does not result in enough energy to use (but the counterspell action works normally).