This robotic sentry unit will most likely leap into the air and deliver a physical attack with moderate damage. It will use an attack called EM Field when Zack is staying close. The only way to dodge this attack is either staying really close to it or staying far away. Staying close to it will somehow force the Guard Spider to stand still, making it easier for Zack to land a few critical hits.
To achieve quick victory against this foe, one should equip any accessories that will boost Zack's MAG and MP, then attack the Spider with Thunder spells. Also, any hits inflicted on its abdomen will be critical.