The black-bladed knife

The black-bladed knife is a knife that can seperate a shadow from the thing that casts it.

Malcolm saw it for the first time when he was seven and his grandfather used it to show him the supernatural is real. After his grandfathers shadow put Malcolm in danger, he made the blade disappear.

Continuity
The knife appears for the first time in episode 07 - Paisley, or: The Man Who Stands In The Shade Of The Cypress Tree. It returns in episode 08- Queen of Cups and is revealed to be in Alecs possession.