Detect Invisibility. Within 60 feet of the tressym, magical invisibility fails to conceal anything from the tressym's sight   Familiar. With the DM's permission, a person who casts the find familiar spell can choose to conjure a tressym in stead of a normal cat.   Keen Smell. The tressym has advantage on Wisdom (Perception) checks that rely on smell.   Poison Sense. The tressym can detect whether a substance is poisonous by taste, touch, or smell.