Possible Clues:

• Nightmare dunderhead and bore...
• King had one hand, finally, on paper
• Visions of sugarplums, perhaps
• Switch off short play about end of battle
• Reason for talking in one's sleep
• Just imagine what you might do if you 1 down
• "A Midsummer Night's ___"
• 'It was all a ___/I used to read 'Word Up' magazine'
• Large amount put on wrong 16 across? Singular 4 16 across, maybe
• Subject of a painting by Picasso or Rousseau