Oil of Diminution is an uncommon type of Potion that can be briefly coat a weapon.
Gazing through the glass bottle, everything seems shrunken and contracted - almost gaunt.
Properties
Potions
Single Use
Rarity: Uncommon
Weight: 0.3 kg / 0.6 lb
Price: 90 gp
Effect
- Coat your active weapon for
Duration: 10 turns. - It receives a -1 penalty to damage, but targets failing a Constitution
Saving throw suffer 
Disadvantage on Strength Checks and Saving throws. - They also a receive a -1d4
Physical to melee damage.