Rusting Grasp

School: transmutation
Circle: ancient 4th
Spell Components: V, S
Action Time: 1 action
Range: touch
Shape: touch
Targeting: hostiles only
Base Duration: quick
Saving Throw: no
Spell Resistance: no 
Ritual Components: n/a

Lays an aging hand on target wearing metal anywhere but held equipment, dealing 3d6 acid damage and bestowing -1 to AC. If caster has greater spell focus: transmutation, instead bestows -2 to AC.