Bag of Protection dust

This small packet contains 1d8 + 4 pinches of dust. You can use an action to sprinkle a pinch of it in a in closed shape. In said shape is an area where you can only enter safely with the protection spell. 

If you enter without the spell then you take 1d10 necrotic  damage every round until you leave the barrier. 

Notes: Damage: Necrotic, Damage, Consumable