Is there some sort of formulae or guidelines on creating ghosty magi like the ones in Broken Covenant of Calebais?
I'm interested in creating some ghostly magi for several character concepts (magus Plagued by his ghostly parens, a Verditius necromancer/spirit master, a ghostly Librarian magus).
In ArM4 SoI: The Greater Alps Tribunal, Timothy gives a formula for creating ghostly magi in the Coveannt of Twisting Shadows using: Creo + Vim + 10 and commenting that Magic auras add to a ghosts Magic Might.
None of the ghostly magi in Calebais seem to use this formulae and several have odd Might scores ending in 8, 9, 2 etc which suggests that their Arts scores might have something to do with things as it seems unlikely that they've lost any Permanent Might points. Oddly, some of the Companion ghosts also have Might scores ending in odd numbers.
All seem to retain the Abilities they had when alive - is this correct?
Might Scores are generally a value ending in 5 or 0 (except for Calebais it seems).
Perhaps Might Scores were given a certain Base Value ,
with a Simple Die roll added on.
Upon what do you base this statement? Might Scores are no more likely to be multiples of five than Art scores. Look at Magical Animal Companions, Might of 10 - Size. That leaves the majority of them with Mights that don't end in 5 or 0.
There is a brief sentence in the Criamon chapter of HoH:MC telling you that if you have designed a magus who becomes a PC ghost, then you can find details of how to design him in "The Mysteries: Revised Edition".
I'm sorry, but it is impossible to say more.
Oh, many Criamon -don't- retain all of their skills from life. They shed them as Adulterations.