I was just going through the MafiaWiki and came across this.
Masons by themselves - they will always spawn as a pair, or in greater numbers.
Coroners when there is no Janitor in the game and/or the mode is not Clue variant.
Mason Leader will not spawn from random roles (not including Mafia Variant).
Note: Spies and some other roles such as Sheriffs are exempt from this rule and still spawn even if there are no Mafia-aligned roles or Masons in the game - this, however, is incredibly rare.
So what I have highlighted in Green: am I to understand that Mason Leaders cannot spawn from random roles INCLUDING random any? If this is true then that sucks.
I have prided on myself that my save makes ALL roles in the game a possibility. However, if I am reading this correctly, then Mason Leaders MUST be a defined role in order to play as a Mason Leader.