The arcanist can gain control of a spell cast by another spellcaster. As a standard action by expending 1 point from her arcane reservoir, the arcanist can make a caster level check opposed by the creature controlling the spell. If the arcanist is successful, she can direct the spell as a free action for 1 round, making any decisions allowed by the spell. This only functions on spells that can be directed or changed once they have been cast, such as flaming sphere or spiritual weapon. The spell returns to its owner’s control at the start of the arcanist’s next turn, unless the arcanist expends another point from her arcane reservoir at the start of her turn to extend the duration of control by another round. She can continue to control the spell for as long as the spell lasts, provided she keeps spending points from her arcane reservoir.
Pathfinder Roleplaying Game: Advanced Class Guide © 2014, Paizo Inc.; Authors: Dennis Baker, Ross Byers, Jesse Benner, Savannah Broadway, Jason Bulmahn, Jim Groves, Tim Hitchcock, Tracy Hurley, Jonathan H. Keith, Will McCardell, Dale C. McCoy, Jr., Tom Phillips, Stephen Radney-MacFarland, Thomas M. Reid, Sean K Reynolds, Tork Shaw, Owen K.C. Stephens, and Russ Taylor.