Undermine Armor
1st-level · Transmutation

Casting Time 1 action
Range 30 feet
Components V, S
Duration Up to 1 minute (concentration)
Classes Bard, Sorcerer, Wizard
You unravel the bonds of reality that hold a suit of armor together. A target wearing armor must succeed on a Constitution saving throw or its armor softens to the consistency of candle wax, decreasing the target’s AC by 2.
Undermine armor has no effect on creatures that aren’t wearing armor.
Source: Deep Magic 5e · OGL/Open