There's no saving throw on the spell taking effect, it just works-and there's no saving throw on the damage, anyone in contact with the item when you use a bonus action to inflict the damage simply takes it. Concentration for example, maximum duration, 'no saving throw'? you seem to be missing a lot of basic things on this one. I think you may want to re-read the spell. In the time it takes to remove your breast plate you would have taken 450d8 damage. If the target wants to stop the hurt, they need to spend 5-10 mins (50-100 rounds of combat) taking their armor off or have dispel magic handy. So on a target wearing metal armor, this spell could scale at 9th level to 9d8 recurring damage each round with no saving throw and causes disadvantage on attacks and ability checks.
Phandelver and Below: The Shattered Obelisk Mordenkainen Presents: Monsters of the Multiverse
