Assimilation

The caster instantly ascertains the nature of the spell being cast, bending it to their own will temporarily. The caster makes an arcana skill check against a spell cast by the target, the DC being equal to the target's spell DC. On a success, the caster can cast the target's spell as an action on their next turn, provided a spell slot of level equal to the spell cast is available. This spell is expended and ineffective if a spell is assimilated and no sufficient spell slot is available. 

At higher levels: The caster lowers the DC by 1 for every level above first.