The Scratch Marks left by Survivors spawn slightly/moderately/considerably closer together.

You become obsessed with one Survivor.  When the Obsession loses a health state, your Terror Radius transfers to the Obsession for 30 seconds, and its radius is set to 32 meters.

You are granted the Undetectable status effect for the duration.

The Survivor with the transferred Terror Radius is also considered to be "inside the Terror Radius" for other purposes.

The Killer can only be obsessed with one Survivor at a time.  Undetectable hides the Killers aura, Terror Radius, and Red Stain.

While carrying a Survivor, you suffer no cool-down on missed attacks.
Successfully hitting a Survivor will pause the carried Survivors Wiggling Progression for 2/3/4 seconds.

After hooking a Survivor, THWACK! activates:

The next time you break a Breakable Wall or a Pallet, all Survivors within 28/30/32 meters of your location will scream and reveal their Aura for 4 seconds.