Luck

Rating	Chance	%
+3	1/8	12.5%
+2	1/12	8.3%
+1	1/24	4.2%
0	0	0%
-1	1/12	8.3%
-2	1/6	16.7%
-3	1/4	25.0%

• 
  Cursed
• 
  Awful
• 
  Bad
• 
  Normal
• 
  Good
• 
  Great
• 
  Irish

Luck is a combat variable that allows a creature to deal double total base  damage in combat. As can be seen from the table on the right, there are three levels in luck modifier: positive (+1), good (+2) and excellent (+3). Luck can also be neutral (zero), which means that a creature stack cannot get a "lucky strike". Creature stack's luck modifier depends mainly on hero's luck status, but can also be affected by spells (Fortune, Misfortune) or creature abilities (e.g. Devils). Additionally, The Shadow of Death expansion introduced magical terrains that can affect luck modifiers. Hero's luck depends on equipped artifacts, possible luck secondary skill and/or visited Adventure Map locations.

Luck affecting features

Adventure Map locations:

• Faerie Ring increases luck +1 until next battle
• Fountain of Fortune gives random amount of luck from -1 to +3 until next battle
• Idol of Fortune increases luck +1 until next battle on odd days (+1 to morale on even days, and on day seven gives both luck and morale +1)
• Mermaids increases luck +1 until next battle
• Rally Flag increases luck +1 (and morale +1) until next battle
• Swan Pond increases luck +2 until next battle (also causes hero to lose all remaining movement points for the day)
• Events may increase or decrease luck from -3 to +3.
• Pyramid decreases a hero's luck by -2 if visited after the guards have been defeated.
• Clover field increases luck neutrally aligned creatures by +2
• Cursed Ground entirely disables luck effects.

Artifacts:

• Cards of Prophecy increases luck +1
• Clover of Fortune increases luck +1
• Ladybird of Luck increases luck +1
• Still Eye of the Dragon increases luck +1 (gives also +1 to morale)
• Pendant of Courage increases luck +3 (gives also +3 to morale)
• Hourglass of the Evil Hour negates all positive luck.

Buildings:

• Rampart's Fountain of Fortune increases luck of defending hero by +2 when defending against siege.
• Rampart's grail building Spirit Guardian increases owners all heroes' luck by +2.

Creatures:

•  Devil decreases enemy luck by -1
•  Arch Devil decreases enemy luck by -1 (-2 with HotA)
•  Halfling always has luck value of at least +1

Miscellaneous:

• Luck secondary skill increases luck by +1, +2 or +3.

Spells:

•  Fortune increases luck by +1 or +2 (or +3, if the hero has a specialty in fortune)
•  Misfortune decreases luck by -1 or -2.

Horn of the Abyss

• Negative luck was introduced; while under effects of negative luck, the stack has a chance (-1: 1/12 -2: 1/6, -3: 1/4) to cause half the damage
• Hourglass of the Evil Hour neutralizes luck only if it is positive
• Luck triggered in combat now increases damage by exactly 2 times, instead of adding +100% to base damage alone
• Triggered luck or bad luck now changes the damage inflicted on every target hit, instead of just one
• Creatures in battle without a hero can now be subjected to the effect of good and bad luck (originally, luck never worked for creatures without a hero)
•  Arch Devils decrease enemy luck by 2 (instead of 1 from the original)
•  Leprechauns double friendly unit luck chance
• Runes of Imminency decrease enemy's luck by 1
• Demon's Horseshoe decreases enemy's luck by 1
• Shaman's Puppet decreases enemy's luck by 2
• Mineral Spring grants +1 luck until next battle and +600 movement points until the end of the day
• Fields of Glory magical terrain gives all troops -2 luck

Trivia

In the game files, Luck variable values have names: Cursed (-3), Awful (-2), Bad (-1), Normal (0), Good (+1), Great (+2), and Irish (+3). This is most likely a leftover element of Heroes of Might and Magic II: The Succession Wars.