Bag of Lava

This item is a bag of lava. When tipped upside down lava does not flow out of it. You can insert any item into the bag of lava and have it catch fire or immediately burn to ash. If a humanoid creature or  monster is put inside the bag of lava, they take 1d12+6 fire damage per round. They take the damage when they enter the lava bag and at the start of their turn. 

Notes: Does not require attunement