Irregular Size

Transmutation [curse]
Level: Antipaladin* 3, Artificer * 3, Bloodrager * 4, Cleric */Oracle * 3, Shaman * 3, Sorcerer */Wizard * 4, Warlock * 3
Components: V, S
Casting Time: 1 Standard Action
Range: touch
Target: creature touched
Duration: permanent
Saving Throw: Fortitude negates
Spell Resistance: yes
  You curse a creature so one set of its limbs (typically its arms, legs, or wings) shrivels in size. Arms: The creature counts as one size category smaller for the purpose of determining the size of weapon it can wield. If the creature is capable of making natural attacks with its arms, the damage dealt by those attacks decreases as though the target were one size category smaller than its actual size.