A creature of the night
It shows itself once, then comes only at night. After a few nights it starts appearing in daylight — first watching, then hunting. You will know it is close before you see it: the world goes quiet.
It learns from you
Every ability it gains, it gains because you showed it how. Open and close your door and doors stop being an obstacle. Walk past your animals and it understands they matter to you. Sleep, and it learns that a body can be left behind.
Everything is saved with your world. It is faster every time you meet it — and it writes down what it sees. Some nights you wake up to a sign near your bed with a line from its notes on you.
The totem will not save you
At the killing blow it takes the Totem of Undying from your hand, blackens it and shatters it mid-air. There is exactly one totem in the world it cannot touch. Find it.