Halloween events for Paper, Spigot & Purpur 1.21.3–26.x: scare events, pumpkin bosses, animated grave waves, Herobrine, candy economy, statistics, Discord webhook, season scheduler. Free & open source.
The Pumpkin Skeleton Boss with its health bar, titles and cursed-bat minions
Undead wave with the wave bar (mobs left, countdown)
The glowing reward chest after the curse is broken
Fence + carved pumpkin altar, lit with flint & steel
Lapis block + carved pumpkin altar
Villager turned Pumpkin Trader with config-driven trades (candy, pumpkins, emeralds)
Loot and XP for the winner