At the start of the Trial, 4 random Hooks are changed into Scourge Hooks:

The Auras of Scourge Hooks are revealed to you in white.
Each time a Survivor is unhooked from a Scourge Hook, the following effects apply:

The Auras of all other Survivors are revealed for 5/6/7 seconds.

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.

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.

While carrying a Survivor, increase your Carrying Movement speed by 6/12/18percent.  Increases your Terror Radius by 12 meters.

The Entity blocks a window for 20 seconds after a Survivor performs a rushed vault through it.

The Hex effects persist as long as the related Hex Totem is standing.

Each injured, dying, or hooked Survivor afflicts Survivors with a stack-able 1/1.5/2 percent Action Speed penalty to Repairing, Sabotaging, and Cleansing, up to a maximum of 4/6/8 percent.
Increases the Action Speed penalty by a further 12 percent, if there are 4 Survivors, who are either injured, dying, or hooked at the same time.