Complex sentence: "Pierce" is furious at the inactivity, and releases the stop time spell; this gives Neil an action, using it to have Duquense destroy the amulet "Pierce" wears with his sword.
Split into simpler sentences: Pierce is furious at the inactivity, and releases the stop time spell. This gives Neil an action, which he uses to have Duquense destroy "Pierce's" amulet with his sword.