Golem Sapper

This octagonal device is roughly fist sized and weighs 1/2 pound. As an action, you can place the device on a construct within your reach. When you do, the creature must make a DC 18 Constitution saving throw. On a failed save, the creature takes 2d10 necrotic damage and is stunned until the start of your next turn, at which point it can repeat the saving throw. Each time the creature makes this saving throw after the first, the DC is reduced by 2 (to a minimum DC of 10). On a successful save, the device falls from the creature and can't be used again for 1 hour. The device's saving throw DC remains reduced after being used. The DC increases by 2 for every 24 hours it isn't in use, up to a maximum DC of 18.