Sometimes the title says it all. This puzzle is themeless, so there won't be a select group of long entries with some commonality to them. (In fact, there won't be any "long" entries at all -- every entry here is 7 letters or fewer.) And it is hard! Expect it to be much more difficult than the ones you've seen so far, with more vague and tricksy clues, and more uncommon answers even when clues are straightforward.
If you're familiar with Fireball Crosswords or the Saturday Stumper, this is my attempt at that difficulty stratum, though I probably undershot a bit. If not, let's say it should be no easier than a standard New York Times Saturday puzzle, and ideally will be noticeably more challenging than those. Take it a little bit at a time. Don't be afraid to fill in a guess if you're not sure, and don't be afraid to erase (if on paper) or backspace if a good guess doesn't pan out.
With that out of the way:
Download as pdf
Download as .puz (for Across Lite)
Note: After today, I will be on puzzle-posting hiatus for next week and the week following next. Expect Puzzle 7 to drop on or around Sunday, December 22. Apologies for the delay.