If the trend continues, and it does occur again, larger ideas would need a longer time to implement....
...
Fantasizing is a major part of this forum's activities! So let's list some ideas we've had for this year's celebration. Forgive me if this has been posted elsewhere already, I do my best to search around but everyone makes mistakes.

Obtain the following by grinding for tokens, trading E for boxes in the SD, or special drops...

Some ideas my group of friends and others have come up with:
(These would be in addition to the traditional punkin king smashing):
Dark Harvest Proposal

For Halls:
Black Snipes, snipes on a (perhaps leafless, dead-looking) tree. Single Snipes: Lazy, flying, wandering. I love these little black birds, they can be seen roosting on the shoulders of Maskwell too during the dark harvest. Crows/Ravens, so cute in snipe form.
Wandering gourdling
Various squashy, gourdy furnitures. And jack-o-lanterns for lighting.
EDIT: adding some more ideas here:
Pacified Howlitzer. It won't make any noises, but, it will still track the movements of the nearest knight. They could also work as a light source. Different varieties for the tiers and statuses, yes please.
Pacified soul jelly. Tis the creepy season.
Grimy Candles - the greenish sickly ones you see around Legion of Almire.
Punkin King mini boss statue - A new boss token item, something like a "Harvest Treat", would be the vital boss material used in making his statue (like Snarbostuffing, etc.). This would be exchanged for a large number of candy tokens. Since it's a mini boss statue, we could have the number of vital Harvest Treat materials be 32 (half of the regular boss trophies), and not have a preceding bunch of statues be consumed in its making.

Weapons:
-Nitronome reskins: exploding jack-o'-lantern, exploding witch cauldron
-Scythes/sickles (suggested elsewhere many times). A guild wars 2 inspiration for potential design: you have regular scythes, black/white/grey, that act like troikas, swinging them around. Charge: twirl it in front of your knight, dealing knockback and maybe harvesting a soul or two. Then you have a scythe called "Slice of Night" - similar to the Gw2 "twilight" sword (only minus the red...) - the blade of the Slice of Night appears to be a sort of portal to a starry night sky, and maybe the afterlife...you really have to look at a video of the GW2 twilight/sunrise/eternity blades to get the picture. Yes, this is sk, not guild wars, but the concept of the art would be awesome. The "Slice of Night" scythe could deal poison, or maybe even be another curse blade like Faust, if it's nice and exclusive, on the charge. I suppose it would need a bit of pink, like lopsided asymmetric eyes all over the shaft (that kind of thing is always disturbing), if it were to cause curse. Slice of Night...Sliver of the End, for poison...curse. Lots of scythes. Better tools, better harvest. To keep it super logical, we could have all the scythes deal pure normal dmg, instead of intuitive shadow. Being unpredictable is scary, right?
-Spur/Arc Razor/Winmillion reskin: Wishing Wand (for the fairy princess).

Personal Aesthetics:
Fall recolors – would be a similar shade of red to the yellowish hallow (or even an inverse hallow coloring).

New costume helms: Authentic Howlitzer Mask, Authentic Bombie Mask, Authentic Devil mask.
Howlitzer: T3, nose horn and all.
Bombie: normal, no status bombie splodies.
Devil mask: you will look like a pit boss. Comes with glasses, but not a mug.

Cthulhu mask. Oh lord yes. Pair this with some dusky dragon wings...

Wanted: Forever Trojan Disguise. A trojan’s grief, a trojan’s curse, is everlasting.
Pet Costumes – have them wear little witch hats, hold trick-or-treat bags, etc.
Bombie disguise. Ewwww. Not just head, full body.
Witch Hat, Wizard Hat, Princess tiara. Classic costumes...at least on Earth... We're knights...who and where is our princess? Let's dress up like her maybe! (Lol Logic).

Reaper set - reaper cowl, reaper cloak. These would be all raggedy and shadow particle-y like a reaper, or even a dementor (Harry Potter fans). The wispy fabric bits will trail behind a knight as they walk. Something special - a knight's eyes won't show up in this cowl. Personal color doesn't show up either. Very scary, the darkness within the cowl...an enemy can't read/predict a face that it can't see! Other details: hands would look a bit like claws, or skelly fingers (thin). Cowl would have spectral chains instead of beads+string. Feet would not have a lot of detail, in order to detract attention from them (pretend to float). Cloak doesn't have an aura slot, as this is occupied by swirly shadowy particles. It has armor back, (shadow wings will match the cloak), armor rear, and armor front. The hood has standard 2* hood slots. So yes, you could do glow eyes (or other prismatic acc to have personal color show) and be interesting. Look into my souuuuuul. Heck, if you're pinkish for your personal color, you could pull off a swarm look.
Nah, scratch the no-aura slot. Simply because ppl don't like accessory limits, and, imo, haunted aura would be way too appropriate for words. Instead, we'll have a separate Shadow Aura, which douses the wearer in swirling shadow particle effects (see the snarbolax to get the idea), and limit the reaper cloak's particle effects to the fringes of the fabric.

These could be available along with the classic Authentic masks, however, they wouldn’t be obtained with punkin king candy tokens…see werewolvers below.

Accessories:
aura- chains. Similar to Cold Iron Vanquisher chains, but a few different styles. Golden, Shadowy, gray.
aura- Candy Corn aura (like sprinkle but, yeah, candy corn)
Crown of Midnight (shadowy, dark version of crown of winter/summer)
Capes – Dracula style to fit the theme. Clipping with wing issues?
Curved Vertical Vents. These would look like devil horns. Maybe have a bit of smoke comin out the top of volcanic ones.
Halo - Forsaken Halo. This would look like the Crown of the Fallen (Valkyrie) helm halo. So yeah, Fallen Helm ppl could have a dark halo around their ponytails and on top with this accessory. Ha. ha.
Footprint (an accessory not currently in the game): armor foot, new slot. Fiend Footprints - regular, shadow, and prismatic. the regular ones are purple. These footprints will be shaped like glowing horseshoes, and whisper of Ur. They would remain behind the knight for a few moments, resulting in a trail of about 5 footprints that fade away over the duration. Possible: in addition to prints, the soles of a knight's feet, on the actual armor, will glow in a horseshoe shape. Shadow shows up just barely for most armors.
Tail: Devil Tail. Like a cat tail in movement, but has a pointy end-bit, classic cartoony devil tail. Looks best in toasty or volcanic!

Shadow Recolors. Come on <3 <3 <3 :3. Or more shadow art, (like costume textures as seen with some promos such as Danger and Stormy).
Wanted: Shadow Salamander Set. Nice and dark, with glowing orange claws. DMG bonus vs. Swarm? lol. Swarm isn't shadow...but it would be neat. Alternative: all dark grays/blues/blacks, no orange glowing bits. Very black claws shed dusty shadow particles.

Usables:
Costume Cauldron -either a confetti or...Idea inspired directly by Guild Wars 2.
Partaking in this boiling brew will turn you into a random undead/fiend monster for 5 seconds. A sort of confetti.
Possibly make this a guild-only thing - and have a person plant a cauldron in a public space, like haven. 100 crowns for 1 second, donate more, costume lasts longer, relevant to amount of cr. Costume will only last as long as you stay in an area - loading into a new area removes it. Crowns go into treasury of the guild that planted the cauldron. Will say "Member's cauldron collected X crowns" in record, crowns will appear after cauldron expires. Cauldrons could be planted for 10 minutes or so. Biased to large guilds. Non-guildies can use, just not plant... Available in Supply Depot for some sort of amount. Just a rough idea.

Other:
New soundtracks for the spooky season, like SK-style "This is Halloween", and so on, for specific fights, like the Punkin King stages.

Monsters:
Gremlin Witch. A more feminine, offensive counter to the gremlin mender: the staff of the Witch, while retaining the mechanical wrench qualities, will shoot lasers in a magical manner. The way only gremlins can.

While the poster below suggested purple projectiles, I think that having the actual mineral in the wand be different colors than mender (not yellow/purple) - say, blue for lower tiers, and red for higher tiers, would help ID this enemy more. The projectiles could be purple in the center, rimmed with red or black, for extra spookyness. Or they could even have a little gremlin-lookin skull in the center. Don't mess with witches! Gremlin witch can spawn in replacement of any thwacker gremlin, and attempt to mess with knights. Could have a special drop table, say, the only monster to drop forge crystals, or the relevant confetti of the event. Firing speed: as fast as a standard Knight alchemer, so watch out!
Style of witch: swampy voodoo, classic pointy hat, or sexy style? Hmm. Which would fit SK the best? Yes, "witches" and "sexy witches" are different monsters. The film "Cabin in the Woods" really nailed that...starts muttering about this tangent...

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Game Mechanics: Wanton Werewolvers
This could actually occur at any time OOO feels like, similar to the Kataclysm. But the DHF could be a great way to start it off, especially for older players looking for something new to do. (Cradle's lunar cycles seem suspiciously similar to irl Earth's if so).

For those unfamiliar with werewolf legends (NOT twilight ones, and not just cliche/standard humanoid only ones), there are many different kinds of werewolves, be they doctor who aliens or an original (animal) wolf that comes into power. To cover the span of the myth, there will be three different kinds: geo knights turned werewolver, true werewolver, and wolves afflicted with the werecurse (less powerful).

Werewolvers
The Geo Knights have been attacked by a cursed wolver pack! Like some of the kat tribes of old, these wolver packs seek power – and got it by chomping down on a chemically unstable moon-bulb in the roof of their habitat. How did they get up there? The most powerful pack alphas concentrated their bloodthirsty minds, and warped up to the rafters surrounding their dens. When they returned, they “blessed” their pack members with the “power” of the moon-bulb, which they have always howled at without knowing why. Or so the story goes. More research shows that this particular moon-bulb had a lot of concentrated energy in it, as well as an unhealthy amount of cheese.

With the harvest moon-bulb at its brightest, several geo knight bases were attacked by packs of these Werewolvers, and several of them have been…bitten. And they have…changed. The packs roam the depths in groups, but our poor geo knights wander alone in any moonlit passages, with a tendency to bite. And the alphas are the most ferocious of all.

Alpha werewolvers will appear as bipedal, shadowy-colored (though not as dark as the swarm of course) brutes in clockwork tunnel depths only. Think like, snarbolax. Dark dark blues. They spawn in special rooms, (like the Punkin King) . Defeating an Alpha Werewolver will take a lot of skill. Attacks would include a lunge (like the zombie), a claw swipe (like the zombie), and a Howl (which stuns in a radius). A special attack, that it only uses after a howl, will have the beast on all fours charging a knight with the intent to bite (yes that’s a miniature poem). This will curse/poison a knight in T3, and only poison in the lower tiers. Attacks will be familiar, but MUCH faster than a zombie, and tracking. Since it is a wolver at heart, it will still auto-dodge many attacks with warping or side-swooshing (tier dependent). A ferocious opponent indeed!

Geo Werewolvers will be smaller, blue bipedal monsters. Upon defeat, the same animation that health-restores a knight will occur, but instead of being all furry and fangy, a geo knight will stand in its place, and thank the knight for “knocking some sense into them” and will “try to head to the nearest medical station.” They have an “aura” that constantly sheds bits of blue fur around them (like sprinkle). The idea is that the werewolver bite is a curse that is everlasting if a knight is bitten while their guard/mental fortitude is down (like, say, a sleeping geo knight camp…) but a revive cures the worst of it. The geo Werewolver is too tough to be taken down by regular clockwork monsters, and too bloodthirsty to use their head and get him or herself to the nearest Spiral Hospital. The attacks for a Geo Werewolver match that of an Alpha Werewolver, but they are less powerful, slower, and they do not auto-dodge attacks.

The “blessed” wolves in the Alpha Werewolver packs will spawn in groups of 3, and be the same shadowy color as the alphas, but won’t have the bipedal nature. Their attacks and behavior are just like regular wolver attacks, but much faster, and dealing more damage, with a low chance to curse in T3. However, they are rather large due to their power, looking like the alpha wolvers you see accompanying Maulos in Heart of Ice. Except not invincible, and shadowy. Tokens will drop when the last of the three is defeated. Maybe make these more common in wolver dens?

All eyes of these Werewolvers glow blue like the moonbulb.

The damage type of all the above Werewolvers deal shadow/piercing damage. Perhaps the Radiant Silvermail would be an excellent defense against these mysterious blood beasts.

Drops:
Tokens: all werewolf related, and so expire with the waning of the moon-bulb cycles below.
Fur: dropped by the Geo Werewolver when you knock some sense into them. Bombie mask. (shedding, exploding, why not)
Claws: dropped by the Blessed werewolvers. Devil mask.
Fangs: Alpha werewolver drop these. Howlitzer mask.

Special Rewards: everyone loves that rare rare drop. Everyone loves the grind...
Alpha Werewolver: shadow wolver tail. Alternative form: tail could have orange glowy spikes along it, to look like Snarby Mommy, or just be shadowy.
Blessed werewolvers: moonlit wolver tail (would be like a cool wolver tail, but with glowing blue swirls in the fur, and shedding blue sparks - similar to volcanic animation)
Geo Werewolvers: "feral fur" aura. This makes a knight seem to be shedding strands of fur all around constantly, sticking around like sprinkle. Prismatic?
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As always, list your ideas for the event in addition to suggestions for the listed suggestions.
In the spirit of the scary season:
"They're eating her! And then they're going to eat me! Oh my Vooooooooooooooooooooooooog!"
EDIT: added to list.
EDIT: Amnimonus idea list