For an upcoming home game, I came up with the following item and am wondering if the rarity is right.
Wondrous item, very rare
A pinch of these dull-grey sands dispels any active magic effect and disrupts permanent magic for 1 minute. It is highly prized by assassins, criminals and thieves.
If you throw a pinch on a person with a ranged attack, all active spells are dispelled and active magic items cease to function for 1 minute and both the user and target must make a DC 10 Charisma saving throw or they age 1 year. Once used, the sands vanish into nothingness
I initially thought it should be rare by comparing it with a rod of absorption which absorbs spells as a reaction (and can convert them to spell slot), but it requires attunement.
The sands shut down everything, meaning you can shut down any magic item out there. That very super-versatility is what made me bump its rarity.