Possible Clues:

• Threat punctuator
• The end of a threat to get zero new reels
• End of an ominous threat
• '...unless you want some bad, bad things to happen...'
• Common conclusion of a 31 Across
• Threat ending (2 words)
• Otherwise making a threat?
• "Alternately ..."
• Ending that threatens
• Backup introducer