Pactbound Armor

Armor (any light), uncommon (requires attunement by a warlock)

This scarred armor is a testament to ritualistic flagellation. Whenever you would expend a warlock spell slot to cast a warlock spell you know while wearing this armor, you can cast the spell at its lowest possible level by expending warlock Hit Dice instead. When you do, you expend a number of Hit Dice equal to the spell's level. This property can be used twice, regaining any expended uses of it daily at dawn.

Take from me my flesh. I only ask for an ounce of your strength in return.