Awakened Gauntlets of Entropy

Oxidized bronze gauntlets so corroded, the fingers are locked in place. Upon equipping them, the rust fades away and the gauntlets appear as though they were just polished. The gauntlets have 15 charges that recharge 1d10 at the beginning of every day. 

You can make an unarmed attack on a creature, on a successful hit you can expend charges to cause a creature's non-magical weapon, armor, and metal items to permanently rust. Non-magical weapons take a permanent and cumulative -1 to damage rolls per charge. If the weapon reaches a -5, the weapon crumbles to ash. Non-magical metal armor or shields take permanent and cumulative -1 to AC. If armor is reduced to an AC of 10 or a shield +0, it is destroyed. You may also expend charges to perform the following actions. 

Anathema - (3 charges) You can cast Bestow Curse without requiring Concentration to hold it. When you kill a creature while they are cursed, you regain 6d4 hitpoints.  

Attenuate - (DM's Discretion) You curse a target's magical weapon or armor to seize, disabling its magical properties and bonuses. The number of charges needed vary on the power of the item. Weapons and armor that have been Attenuated can be rusted as if it were non-magical, but it must be done as a separate action. 

Adulterate - (5 charges) If you are hit by a spell, you can use your Reaction to attempt to corrupt it and use it against your foes. Make an Intelligence check and if your roll is higher than the enemy spellcaster's Save DC, you redirect the now corrupted spell towards a target of your choice (target(s), range, and other attributes depend on the spell) and that target takes half of the spell's original damage/effect. On a failed Intelligence check, the spell is still absorbed into the gauntlets, and you suffer half damage/effect.

Annul - (10 charges) You can make an unarmed attack in an attempt to grab a creature. On a successful hit, the target must make a Constitution saving throw (DC 20). On a failure, the target takes 20d8 Necrotic damage. If the creature is killed they become a shriveled, mummified husk and you regain hitpoints equal to half of the damage caused to the target. 

As for rusting large metal items/objects such as doors or cannons, the amount of charges it takes is up to the DM's discretion.