Chill effectiveness

• Unit chill effectiveness determines the attack rate and velocity modifiers applied when chilled by applying cold length, or freeze length or Freezes Target to units other than normal and minion monsters.
• Also determines the maximum attack rate and velocity modifiers applied by Holy Freeze: level 12 Holy Freeze may apply -50 attack rate and velocity to targets with -50 chill effectiveness, but it only applies -25 to targets with -25 chill effectiveness. [1]
• Bone Wall and Bone Prison have 0 chill effectiveness, while all other hirelings and pets have -50 chill effectiveness (like players).

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0 Chill effectiveness

• Following monsters always have 0% chill effectiveness, resulting in no attack rate or velocity reduction when chilled (radial cold damage of Holy Freeze also doesn't apply, although its cold attack damage does if the target is not Immune to Cold):

Korlic Talic Barricade Barricaded Door Barricaded Tower

Catapult Death Lord Diablo bone prison Evil Demon Hut Fire Tower

Lightning Spire Mummy Sarcophagus Prison Door Trapped Soul Window

• Frozen Scourge have 0 chill effectiveness in Normal, as do all Frozen Horrors in Nightmare, but all those in Hell have 33 chill effectiveness: Holy Freeze does not apply radial cold damage, attack rate or velocity modifiers, but being chilled would increase attack rate and velocity if they weren't always Immune to Cold. [2]
• Gargoyle Trap has 0 chill effectiveness in Nightmare and Hell.
• Following also have 0 chill effectiveness in Hell:

Andariel Bone Fetish

Flying Scimitar Night Marauder

Willowisp Wraith

Normal

-15	-20	-25	-30	-40
Baal Baal clone Frozen Abyss Frozen Terror	Duriel Abominable 1 Snow Drifter	Andariel Diablo Mephisto Madawc Frozen Horror 2	Blood Lord 3	Night Lord

¹ Spawn as normal in Frozen River, and as Champion or Unique in Glacial Trail.
² Spawn as normal in Crystalline Passage.
³ Spawn as normal in Abaddon, and as Champion or Unique in Worldstone Keep Level 1.

• All other monsters not listed above have -50 chill effectiveness.

Nightmare

-10	-15	-20	-25	-30	-33	-40	-50
Frozen Abyss	Andariel Baal Baal clone Diablo Mephisto Abominable 1 Snow Drifter	Duriel Blood Lord 2 Hell Lord Moon Lord	Madawc Flying Scimitar Night Marauder	Night Lord	Izual Abyss Knight Bone Fetish Council (Act 3) Doom Knight Greater Mummy Oblivion Knight Reanimated Willowisp Wraith	Claw Viper Sand Raider	Maggot Egg

¹ Spawn in Drifter Cavern, Ancients' Way and Icy Cellar.
² Spawn in Abaddon, Pit of Acheron and Crystalline Passage.

• All other monsters not listed above have -40 chill effectiveness.

Hell

-5	-10	-15	-25	-33	-40	-50
Frozen Abyss	Diablo Diablo clone Mephisto Uber Diablo Ub Mephisto Abominable 1 Blood Lord 2 Hell Lord Moon Lord Snow Drifter	Baal Baal clone Uber Baal Madawc	Duriel Uber Duriel Night Lord	Izual Uber Izual Abyss Knight Council (Act 3) Doom Knight Finger Mage Giant Spider Greater Mummy Mummy Oblivion Knight Reanimated Scarab Demon Skeleton Skel Archer Skeleton Mage Vampire Zombie	Claw Viper Sand Raider	Maggot Egg

¹ Spawn in Drifter Cavern, Ancients' Way and Icy Cellar.
² Spawn in Abaddon, Pit of Acheron and Crystalline Passage.

• All other monsters not listed above have -33 chill effectiveness.

Reference

• Onderduiker, Chill Effectiveness (Technical Discussion)