Expose Weakness, also known as Guard-Off, is a recurring Blue Magic spell.
Guard Off (called Off Guard in some translations) is a Blue Magic spell that lowers enemies' Defense. It can be learned from Page 256, Magic Dragon, Shadow, Ziggurat Gigas and Azulmagia. It cost 19 MP to cast. Ushabti, while technically having the attack, can never use it as it cannot have enough MP to use it.
Expose Weakness is a Blue Magic spell learned from Fire Drakes that reduces a unit's Defense and Magick Resistance. The spell costs 8 MP to cast and can hit a target up to 4 tiles away from the caster.