Halloween season

Wrath Cookies' appearance during Halloween

Halloween season is a seasonal event in Cookie Clicker. It begins on the 24th of October and ends on the 31st. Alternatively, it can also be activated at any time by purchasing the "Ghostly biscuit" switch, which is obtained by unlocking the season switcher, a heavenly upgrade that costs 1,111 heavenly chips.

The Halloween season features seven Halloween-themed flavored cookies and changes the appearance of wrath cookies to look like frowning jack-o-lanterns. The Halloween cookies can only be obtained by popping wrinklers, meaning the One Mind upgrade must be purchased first in order to obtain them.

Upgrades

List of the 7 known flavored cookies which may drop from Wrinklers during the Halloween season. Each flavored cookie has a base cost of 444,444,444,444 (444.444 billion) cookies.

Icon	Name	Unlock condition	Base price	Description	ID
	Skull cookies	Minimum 5% drop chance from popping a wrinkler during Halloween season	444.444 billion	Cookie production multiplier +2%. "Wanna know something spooky? You've got one of these inside your head RIGHT NOW."	134
	Ghost cookies	Minimum 5% drop chance from popping a wrinkler during Halloween season	444.444 billion	Cookie production multiplier +2%. "They're something strange, but they look pretty good!"	135
	Bat cookies	Minimum 5% drop chance from popping a wrinkler during Halloween season	444.444 billion	Cookie production multiplier +2%. "The cookies this town deserves."	136
	Slime cookies	Minimum 5% drop chance from popping a wrinkler during Halloween season	444.444 billion	Cookie production multiplier +2%. "The incredible melting cookies!"	137
	Pumpkin cookies	Minimum 5% drop chance from popping a wrinkler during Halloween season	444.444 billion	Cookie production multiplier +2%. "Not even pumpkin-flavored. Tastes like glazing. Yeugh."	138
	Eyeball cookies	Minimum 5% drop chance from popping a wrinkler during Halloween season	444.444 billion	Cookie production multiplier +2%. "When you stare into the cookie, the cookie stares back at you."	139
	Spider cookies	Minimum 5% drop chance from popping a wrinkler during Halloween season	444.444 billion	Cookie production multiplier +2%. "You found the recipe on the web. They do whatever a cookie can."	140

The current drop chance is 1-f, where f is the fail rate. The base fail rate is 0.95, or 0.8 if the achievement "Spooky cookies" is unlocked. There are several modifiers which can further reduce the fail rate.

Modifier	Factor
Green yeast digestives	1/1.03=0.970874
Dragon teddy bear	1/1.03=0.970874
Santa's Bottomless Bag	1/1.1=0.909091
Spooky Cookies	16/19 = 0.8421 (relative)
Starterror	0.9
Shiny Wrinkler	0.9
Selebrak, Spirit of Festivities	0.9/0.95/0.97 (Diamond/Ruby/Jade)
Mind Over Matter, Reality Bending, both	1/(1.25, 1.025, 1.275) = 0.8, 0.9756, 0.7843
Cosmic Beginner's Luck	0.2
Garden plants (mature, dirt)	1/(1+0.01G+0.01S+0.03K) G = # of Green Rot S = # of Shimmerlily K = # of Keenmoss

For example, if a wrinkler is popped with the Spooky Cookies achievement and the Santa upgrade Santa's Bottomless Bag, then the fail rate will be:

$f=0.8/1.1=0.727272$

If a shiny wrinkler is popped with Mind Over Matter, Selebrak in Diamond slot and four Keenmoss in the garden, the fail rate will be:

$f=0.95*0.9/1.25*0.9/1.12=0.549643$

Cookie Spawn Probabilities

Upgrade Probability Distribution

Exploding a Wrinkler after it has begun to feed on the big cookie has a 5% chance of unlocking 1 of the 7 Halloween-themed cookie upgrades. If the Spooky cookies achievement is unlocked, it increases to 20% chance. However, if the particular upgrade chosen at random is already unlocked, it will not unlock a new one. So on each Wrinkler explosion, the actual chance of unlocking a new cookie type is equal to:

$s\cdot \left(1-{\frac {N}{7}}\right)$

Where N is the number of upgrades already unlocked and s=1-f is the success rate (0.05 normally, 0.2 with "Spooky cookies", 0.136364 with "Santa's bottomless bag", and 0.272727 with both). The table below shows how the success rate (r) effects the expected value of Wrinkler explosions needed to unlock all 7 Halloween cookie upgrades.

For example, with bare success rate (s=0.05), the expectation value is:

${\frac {363}{20s}}=363$

However, with "Santa's bottomless bag" and "Spooky cookies", s becomes 0.272727 and the expectation value drastically reduces to:

${\frac {363}{(20s)}}\approx 67$

This Desmos graph shows how many wrinklers it takes on average to get all 7 Halloween cookies.

Achievements

Icon	Name	Description	ID
	Spooky cookies	Unlock every Halloween-themed cookie. Owning this achievement makes Halloween-themed cookies drop more frequently in future playthroughs.	108

Trivia

• The Halloween Season was first confirmed on Orteil's tumblr.
• The Halloween Season was added in version 1.039.
• The Halloween Season at first did not account for leap years, so the event would start and end one day earlier on leap years. However, this was eventually fixed in version 2.031.
• The Ghost cookies' text references the Ghostbusters theme song.
• The Slime cookies' text references the movie The Incredible Melting Man.
• The Bat cookies' text references the movie Dark Knight.
• The Eyeball cookies' text references a Friedrich Nietzsche quote.
• The Spider cookies' text references the Spider-Man cartoon theme song, as well as containing a joke about the internet.
• The price of the cookies being four sets of fours because in some Asian languages (e.g., Chinese, Japanese) the number 4 sounds like the word for death.