Shows a threat bar for each enemy whose threat table you're on and shows who has aggro on the mob as well as how much threat until you overaggro.
Requires nameplates to be enabled, otherwise you'll only get a bar for your current target.
You can increase the nameplate range to 41 yards in the Interface -> Names options or by running this command /run SetCVar("nameplateMaxDistance", "41")
If you want to blacklist an npc then you can enter the npc's ID into the blacklist table found in the Actions tab and clicking the red Expand button near the top to open the custom code editor.