Special Charm
The Special Charm is an item that greatly increases the chance for daily Luck.
It is unobtainable in-game as of PC v1.2. It is the item that would appear in the blank space in the player's Wallet between the Club Card and the Skull Key.
Formula
The formula used to calculate daily luck (as of PC v1.11) is:
If player has Special Charm and a random number between 0.0 and 1.0 is less than 0.8 Then Daily Luck = 0.1 Otherwise Daily Luck = a random number between -0.1 and 0.1
Since the Special Charm is unavailable, the last part of the formula always executes. However, if you do have the Special Charm, the formula will give you an 80% chance for maximum daily luck.
Obtaining the Special Charm
It is possible to edit a saved game file and add the Special Charm to your wallet. You must find <hasSpecialCharm>false</hasSpecialCharm>
and change it to <hasSpecialCharm>true</hasSpecialCharm>
.
With SMAPI and its included Console Commands mod, the debug command debug specialCharm can be used.