Yours is an issue very commonly raised by people who don't work with statistics, and a fairly subtle one. In a nutshell, the catch is that we don't really care about distinctions between low rolls.
Look, take any object around you. Its molecules are all moving in random directions -- just for very short intervals of time, before being "pulled back" by the other molecules (if they weren't, the object would be really, really cold). Every set of directions has a very, very small but positive probability of occurring. Right now, one of these sets is occurring, despite the tiny, tiny probability it had of occurring. Do you find that incredible? I believe not.
Another set of directions that would have a similar probability of occurring (I can fairly confidently say another) would be that of all directions pointing towards your head. If that occurred, the object would suddenly grow colder and speed towards you, whacking you in the head. Now, suppose you walk down the street, and a pebble strikes your head from behind. You turn around, and you see an urchin telling you: "Hey, it wasn't me! The pebble's molecules aligned just so". Would you believe the urchin? I believe not.
You don't need to change the rules. You just need a cup to shake dice in and throw them, instead of throwing them by hand!
The point is that if someone can consistently reproduce a result with dice, the dice are not being used as intended by the rules. It may seem pedantic, but when the rules tell you to "roll a die" it means "act on a die so that the probability of each face coming up is roughly identical and roughly indpendent of all previous rolls". Would you complain about Ease factors being way too low if your players could simply take a die and place it with whatever face they wanted facing up (or, worse, if just a small subset of your players could do that, and not the others)?
I think alot depends on the player's OOC mindset as well as the goals of the PC to begin with. I have never myself seen particularly amazing vis studying rolls, and usually the amazing rolls are for something completely silly and almost inconsequential. (Like rolling 78 to walk across a stream with a mild current.)
People are acting like the whole world is going to know this guy has a Mentem of 100+. How would they know unless the PC made his degree of aptitude openly known? Is the PC a Bonisagus bound to share his knowledge and discoveries with the order?
How are Faeries and Demons going to instantaneously know?
Agree, 100%. Unless he whips out his big Mentem no one will know. If his Mentem is 113, and the troupe moves forward to that, he's going to be able to penetrate almost anyone's Mentem resistance. I mean, it won't even be close. He could Peer into the Mortal Mind with near impunity without having to be concerned with voice or gestures (those penalties are effectively meaningless now).
Ooh, think of that Familiar Bond!!! Int+Tech+113+MT+Aura+Lab, and if rebinding add assistance from the familiar. Of course CrMe rituals to boost Int are trivial. That should pretty easily be 4/4/4 or 5/4/3 or 5/5/1 for the Cords.
Well, in our world, being lucky with dice is superstition. As the Random Number Polyhedron is not an in-game effect, some people simply get better rolls than others, and that's pretty much okay.
That said, it's pretty clearly the case that a roll that suddenly shoots a magus up to record-breaking levels of Mentem has the potential to unbalance the story, and a roll like that that's bad for the story is a bad roll. As an SG or troupe member, I'd cut the growth down to a reasonable level and offer an interesting and thematic Virtue as, effectively, a Twilight Scar (because a wild success like that does deserve a nice perk out of the deal). The only time it wouldn't be bad for the story is if we wanted to play a saga around the magus who suddenly rendered the entire existing state of the Mentem Art obsolete by a stroke of pure dumb luck; any other story would likely be hijacked by something that big.
It comes down to the question if the troupe want's a story like that. If they are ok with that go on and make an interesting story out of it.
I would simply discuss this with my troupe.
I have seen people hit multiple "1's" using Invisible Castle. Happened in Ruins of BIbracte saga for a roll a speech a player gave. I have not yet seen it in vis study. Come to think of it, I cannot recall the last time anyone studied vis in a game I was in.
For furtue reference, an easy formula to calculate xp cost and growth using the pyramid system is as follows.
Take the first number in the sequence plus the last number, times the amount of numbers in the sequence, divided by two.
Divide by 3 then multiply by 2 for an Affinity
Multiply total by 5 for Abilities.
No charts or fancy math symbols needed
But anyway, I would also be unsatisfied with a roll that skewed the whole saga like that and would negotiate a different benefit. Even for my own character.
I share your concern. Of course, the definition of skew is undefined. Even if we double his Mentem score (I'm on my phone so reviewing previous posts is hard so serf's parma) to 46 could unbalance the saga. Consider that he need never study Mentem again and he is the most puissant practitioner of Mentem that the Orde had seen heretofore. That is going to change the saga, but certainly not nearly to the degree of Mentem 113 would. The problem is that limiting the roll is unfair from the point of view that the player was willing to accept 5 or 6 botch dice for the proposition of unlimited returns that the RAW allows. How do you resolve the situation post fact while honoring the roll and acknowledging the risks the play character anticipated?
I'd be inclined to roll with it. When Lady Luck (or poorly-engineered dice, whatever) provides you with a minor miracle, I think it feels wasteful to ignore it. And it's not like the game will become unplayable because of his massive Mentem score.
Maybe he decides he's going to invent a Communication-boosting spell, cast it repeatedly, and then write a level 56 Mentem Summa. That'll keep him out of everybody's hair for a while, and his super-book would make a handy MacGuffin. Maybe he hides his power, secretly inventing massively powerful Mentem spells and not telling anybody about them. Maybe he just lives his life as he did before, not interested in the consequences of being powerful. Maybe he decides to use his power to make items, and basically becomes a full-time lab rat while all of his friends get awesome super-items.
Typically when we get a roll like that it impacts SOMETHING related despite the action being rolled being trivial. It's just a matter of storytelling. Something heroic happened, a secret nature unlocked or discovered, an insight gained... At worst some minor virtue is gained.
Take the street urchin. In that moment, for the first time, it becomes intrinsically clear how to manipulate the lock. "I've been doing it wrong all this time", you think, "I've been trying to impose my will on the lock, but if I feel the lock and become the lock, I move myself like..." and the thought drifts away as sudden as it came. Gain Affinity with Legerdemain also let me know next time you sleep, moving on...
I had a Comapnion had a 1 coming up 7 times in a row followed by a 7 on a storytelling roll (she had 3 in communication and 7 (including specialization in storytelling) in Byzantine Greek from the start) so that story made her damnable famous all over greek for her ability and the story became almost more famous than she was. I think in the end I got a +5 reputation by the game master...not bad ehh. At that time I wished that I had not taken the merit Free Expression. She did this on main market square of Athens while waiting for the magi to examine a building.
The damnable part of her famousness was that she became swarmed by greek faeries and gods trying to make her their bard and she got the flaw faerie attention (that did just that, all faeries wanted her to make more stories and did all to get her attention, from giving her ancient gifts and treasures to kidnap her children (or exchange her daughter with a faerie beet (yes the thing you cook from))). And i think you remember from the classics what happens when you say no to Hera or Afrodite...or pick one goddess over the other...
...and yes, maybe it is a good thing to say that she was a devout Hekate worshipper from the start.
That poor bard went through most of the mythologocal bad stuff that all ancient greek heroes and heroines did, together, and then some.
I'd sit the player down with the GM and work something out.
Mentem of 113 is broken and the player might not want that as it'll negate any real challenge. Cap it at 100xp and throw in puissant or deft art (or both) for free so its still really good but not broken. Add a couple of cool twilight scars and certainly have him twilight.
If you do want to go with mentem at 113 (hey, its your game, whatever works) then think hard about how this will impact the game, have the player and GM come to some shared idea of where to go with it. If you mage wants to use that high mentem for all its worth, its going to end up being a major plot driver for the saga. Even a single summae written by that character will be a huge macguffin, everyone will want to know where it came from, are there any more. Theft will be a real problem for a book of that power. Tytalus will want to test that magus, quaesitors will fear that he could mind read other magi with impunity and any mage up to no good will not want him even aware of their existence. At the same time, that level of power could bring demons and fae as noted above.
It could make for a really cool saga IF (IF!) the players are happy to go that route.
You could overflow the experience from Me to other Arts; once the Me is doubled, overflow to Co, then Im, and so on (or just divide by 15, giving you 400+ points per Art), or you could overflow to various mental Abilities, as the magus now has vast and overwhelming insight.
This has the upside of not being so over-the-top, but makes the character generally more able and powerful, which may be less desirable from certain points of view.
Personally I'd be tempted to discuss with the player what breakthrough, if any, they'd like to achieve in mental magic. Then convert a reasonable number of their points into that breakthrough happening.
Suddenly they have the insight needed to make the Parma Magica protect everyone from its wearers gift; or the arts of Corpus and Mentem become one art for them; or Mentem and Auram [the breath of life and all that]; or they can contact the souls of the dead; or eye range becomes equivalent to personal.
Gribble, I'll point out that you are really limiting the results of the roll AND also imposing something punitive on a positive result. Making him twilight, which I did, and made sense to that character and story is certainly punitive. For my NPC there was no cost to him. At his present Arts score 100 xp will move him up 4 points and smacks of the 4th edition limit of no more than 3 increases in scores, which I really detested. Regardless, changing the result without providing substantial XP, and IMO, 100 is not substantial when compared to what he deserves according to RAW.
I'd probably go with suggesting doubling his Art as a cap, and adding some virtue that supports that, that he doesn't already have. Deft Mentem should be selected for any Mentem specialist, it's just too useful, and saves tons of experience in spell mastery. Every Mentem specialist I've built has had Deft Mentem, if he doesn't have it, by all means, have him take it. If he does have it, then a magical focus might be appropriate, this will really magnify his Mentem in some area. Memories seems thematic to suddenly acquiring a vast amount of knowledge. I would even consider The Enigma as a good virtue if he's willing to explore the mysterious aspect of his sudden knowledge. And it might be wise, no matter what the final Mentem score is, to apply it with full effect in the lab and to gradually ramp it up for casting totals, representing that it takes time for him to fully grasp the depth of Mentem knowledge he has. The idea being is you can gauge the effect of the huge Mentem score on the saga and find a limit organically, although it might involve clawing something back...
The idea of converting some of the XP into breakthrough points for a breakthrough is also a neat idea. Of course, if the player/character isn't interested in research...
Something tailored, like Flawless Mentem (a specialized version of Flawless Magic), could also be appropriate. The character learned so much about Mentem that spell mastery now comes naturally to him in that Art.
I'd negotiate it differently. Say they rolled ten "1's" in a row. I'd ask if thy would be a sport and hold some in reserve. Use only two or thee doublers, and hold the rest in reserve to call in any time to double a roll after the fact.
And i think you remember from the classics what happens when you say no to Hera or Afrodite...or pick one goddess over the other...