The concept of mystery cults has evolved over the last two editions. Mystery Cults started out as secretive organizations that allowed a magus to initiate a limited set of virtues relating to historical hermetic/gnostic spiritualism. Most magi in the order didn't even know this was possible. Now we have four houses that are openly acknowledged as mystery cults, several more houses implied to have one or several mystery traditions as an important part of its membership, and several Mercurian splinter groups fighting over anyone who is willing to lose most of their spontaneous magic by initiated the Mercurian Magic virtue. In addition, the list of virtues is no longer constrained.
The question is how to build a balanced cult with the appropriate number of mystical speed bump virtues while still being the invention of an organization of highly intelligent wizards.
There are a number of virtues that are very powerful. On top of my head: Mythic Blood, Flawless Magic, Flexible Formulaic Magic, Strong Faerie Sympathy (+3 to multiple skills, attunement to faerie auras, and the ability to scale up, with appropriate warping, into a mini-exalt), perhaps Major Magic Focus (though most characters already have a focus)and the Gentle Gift. Ability to initiate the last (which I would not allow) would make the cult into a very popular organization within the order). Magi are likely to want to stack powerful virtues together earlier in an initiation cycle to 1. gain maximum benefit from ordeals and 2. insure that the initiate survives to later initiations. I mean, to be utterly horrific from a game balance perspective (and capitalize on the ability to do an ordeal for one initiation and follow it almost immediately by another initiation) I can see both of these cults going around house Flambeau:
Cult of Adventure
Outer Virtue: Unaging (a virtue that benefits the cult more the earlier it is taught)
1st Initiation: Minor Flaw: Heroic Blood (Brave +5, also gives the benefits of self-confidence, character occasional does things without knowing the reason why), Major Virtue Charmed Life (luck + spend a confidence point to escape a botch).
2nd Initiation: Second Sight (Pulling off the bonus from the last initiation) or intuition
3rd & 4th Initiation: Major Flaw: Oath of Fealty to the Black (see BS&S or LotN), Major Virtues The Gentle Gift & Flexible Formulaic Magic (at the same time!) (or Major Magical Focus, The Black). (Both initiated at the same time).
5th & 6th Initiation: Improved Characteristic (Presence) or Great Characteristic (Presence) & Puissant Cult of Adventure Lore (Again both at the same time)
7th Initiation: Transformed Human (Possibly a horrible fate for a Christian magus)
That's probably horrifically abusive but now that I see it wow could it be fun to play.
The Way of the Perfected Spell.
Outer Virtue: Method Caster, or Cautious Sorcerer or Fast Caster or Life Boost (secret techniques to better shaping your magic)(Note multiple options because many initiates already have one or more of these virtues).
1st Initiation: Major Flaw: Necessary Condition (gestures taught by the cult), Major Virtue: Flawless Magic
2nd Initiation: Major Virtue: Flexible Magic
3rd Initiation: Method Caster, or Cautious Sorcerer or Fast Caster or Life Boost
4th Initiation: Method Caster, or Cautious Sorcerer or Fast Caster or Life Boost
5th & 6th Initiations: Minor Flow Vow to Teach Cult Lore, Minor Virtues Improved Characteristic (Presence) or Great Characteristic (Presence) & Puissant Way of the Perfected Spell Lore
7th Initiation Booster Magic (go give this one a hard look, including where it can boost damaging spells to group or above).
For added cheese figure out some way to work Affinity with Parma Magica into a martial art that turns on mastering arcane gestures.
And perhaps the most broken thing I can come up with using multiple initiations at once a mystagugue with +10:
The True Children of Bonisagus
Outer Virtue: Book Learner or Study Bonus
1st, 2nd & 3rd Initiations: Weak Characteristics (split among Str, Sta and Per at SGs discretion), Any three virtues chosen from Improved Characteristic (Communication), Great Characteristic (Communication) and Good Teacher.
4th, 5th and 6th Initiations: Flaw Meddler. Major Faerie Sympathy (Scholar), Secondary Insight and Improved or Great Characteristic (Communication).
7th Initiation: Puissant Intrigue
8th & 9th Initiations: Minor Flow Vow to Teach Cult Lore, Minor Virtues Improved Characteristic (Presence) or Great Characteristic (Presence) & Puissant Cult Lore
10th Initiation: Diedne Magic (Yes the entire thing has been a Diedne trap).
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