Nizbel will hit individual characters with a moderately powerful charge attack, or stomp the ground to damage the entire party with an earthquake for a little bit less damage. Hitting him with a Lightning-based attack will shock him into losing several of his turns, mitigating the physical damage, but a few turns later he will release the electricity, hitting the entire party with Lightning-elemental damage.

Shocking Nizbel will also lower his very high defense so that physical attacks will work against him. Alternately, if you don't have a Lightning-based attack to use against him, any magical attack will be effective whether or not he has been shocked. Ignoring the intended shock strategy and unloading magic on him aggressively is often faster, but make sure you are able to survive his attacks against you.