Sack of Spectral Spiders
Drops from Arachnis. The decorations of the 5 items exist even Hallow's End passed NOW(Asia). I don't know how long the decorations will last.
The 
Sack of Spectral Spiders is a Hallow's End toy obtained by looting Arachnis, a rare NPC found inside player garrisons during the holiday event.
Guide awaiting review
Complete Hallow's End Dailies
During Hallow's End, complete the daily quests from Orukan — Smashing Squashlings, Foul Fertilizer, Mutiny on the Boneship, and Culling the Crew — to earn 
Spooky Supplies. These supplies are account-bound and do not expire, so you can stockpile them for later use.
Buy Creepy Crawlers Decoration
Spend 5x Spooky Supplies to purchase 
Creepy Crawlers from Izzy Hollyfizzle at your garrison. Right-click the item to apply the spider decoration to your garrison, which spawns Arachnis. Note: this decoration persists even after Hallow's End has ended for the year.
Locate and Loot Arachnis
Find Arachnis at 72.84, 36.15 in your level 3 garrison, near the outside of the mine cave. Arachnis is a rare that respawns every 3–5 minutes and awards one loot attempt per character per day. You can also visit a friend's garrison and kill Arachnis there with each of your characters, allowing up to multiple attempts per day across alts. Disable auto-loot before killing Arachnis to avoid a bug where only one item is looted.
Purchase from Vendor (Alternative)
If you prefer an alternative route, Arachnis also appears as a vendor at 55.2, 87.4. The Sack of Spectral Spiders is tradeable, so it may also be available from other players.
Tips
You can visit a friend's garrison and kill Arachnis on multiple alts in the same day to get additional loot attempts — see the video guides for a walkthrough of this method.
The Creepy Crawlers garrison decoration and the associated spider decorations remain active even after Hallow's End has ended for the year.
