I am currently playing in a High Fantasy Saga. There are a multitude of different magi within the Covenant of Semita Errabunda. My first time playing Ars and all I decided to attempt something different. I went down the dark path of Infernalism. Everyone who is familiar with the Goetic Arts is probably already aware of the headaches and rules bickering that comes with the territory however it is a simple question I pose today, is ROP:I too much power for players willing to take the consequences for being infernalists? My SG believes the material was meant for storytelling options for the storyteller and not player character options. My arguement was despite the obvious advantages that come from being an infernalist, after all it is a shortcut for power, there are drawbacks that counteract these benefits. I have already informed my SG that I am attached to my character's story and not just the abilities she possesses. All in all I am wondering what more experienced players and SG's feel about this. Is it something that should be available only for the machinations of the SG or does it indeed provide an interesting story in the hands of a player as well? I really don't mind making another character using the rules from Arm5 core book only, however I just wanted the opportunity to do something out of the ordinary, maybe play a character who could then be used not just as a cautionary tale to others but also the experience that comes from being a diabolist.
On your first dive into Ars Magica?
Not the decission I'd have made.
No.
Infernalism isn't actually all that useful, compared to Hermetic Magic.
And I disagree strongly. However!
If you have an SG (as opposed to playing troupe style), he is entirely within his rights to disallow any element of the game, or to keep something limited to NPCs. I would probably have tried to persuade you away from the infernal for your first character, simply to make sure you understood the basic system.
Why?
Ofcourse there are. Just remember he always has the option of simply killing of your infernalist.
In general, Infernalists work much better with a friendly SG.
I've been trying to corrupt a few characters, and they have generally refused. Compared to some of the other stuff in ArM, I don't see why it should be kept as "NPCs only".
Have you considered the faerie binders from RoP: F?
Also, please break up your text?
This sort of 'Wall-of-Text' is rather annoying to read.
Aha. I am also not very familiar with the art of posting. After looking back...yea too much text so close together. My apologies! 
Thanks for the input, I definitely agree that I made a hasty decision in playing this kind of character. I have indeed looked at some of the faerie binders or sahirs. They are interesting, in fact my SG suggested something along those lines. However it isn't just the Summoning theme I was into but more so the story of the dark hero.
However I am beginning to think this isn't that kind of setting so in lieu of things I just needed to know what sort of expectations I should realistically have an Ars player. Thanks again Tellus I appreciate the response!!
That aspect of the setting is largely up to your SG, really.
I have played and run in a number of Ars Magica sagas and the one lesson I've learned above all is that the game is a negotiation.
As storyguide, I've let players get away with murder against my better judgement and imposed restrictions that we've all come to regret later. So I would slightly reset so you can ask the right questions to get the outcome that's best for the troupe.
I have nothing against players going Infernal. I had the whole troupe doing it once for some sideways stories based on John Post's Life on the Outside scenario. But I can understand the storyguide's unease. Things could get powerful (it's Hell, why wouldn't they want you to be powerful?) but you have to make sure that you're not outshining the other players. There's nothing more important than the troupe.
And I would also put a cap on that character's story. I'm an old-fashioned player and I like to see the good guys win and the bad guys brought to justice. And if you're playing with the Infernal you have to understand which camp you're in. In my game, at some point in the saga, the character will be brought to account. You might agree an ending together, or give the storyguide a free hand to some up with something. However it plays,I'd see the character as one with a finite life. Enjoy it while it lasts, make a good ending, then move on to the next character.
I disagree with your storyguide. There are very few things in the game that are not designed with player characters in mind. I can only think of some of the faerie bestiary archetypes at present. So if the rules are there then they're fair game, just make sure it's the kind of game that everyone is comfortable with.
It's not so much that there's too much power, it's that by trying to be a "dark hero" you are kind of refusing to pay the price for the power. The Infernal's bad news in Ars, not just the sort of "Naughty and Self-interested" you get from Chatoic Evil in some game,s but seriously and actually corrupting and evil. So, if you are playing an infernalist, your character really and truly is committing a sort of slow suicide. Now, that suits certain character types, but if you just want it as a power boost, then you're not using it for what it was designed for, IMO.
With a helpful SG, you can work around that, but you and your SG don't seem to have had a proper play contract conversation.
I don't believe one can be a dark hero if you're an infernalist. Since everything the hero wants to do is based on infernal acts, I don't think any good should come from his good intentions. Sure, things my be fine at first, but eventually whatever he does crumbles around him and he does more evil than good. Save the princess? She later commits suicide, which is worse since by saving her from whatever held her isn't nearly as bad as killing herself later on when the situation is resolved. Eventually, playing an infernalist one's world must crumble in on itself.
I think there's a journey you can take a character on, one that starts with good intentions (there's a saying about those). But you're right that within the scope of the narrative the noble infernalist just doesn't make any sense to me over the long run. Either the character fights to retain their morality, in which case Hell may work against them in order to claim the rebellious soul, or the character gives in to Hell's intentions.
I believe another point to consider is how being an infernalist will affect the other players in the game. Assuming they wouldn't be too thrilled to have an infernalist in their midst, and assuming the people (not the characters) know you are an infernalist since they sit at the same table you do, then when you do something that could be "infernal", they either ignore it (potentially to their own peril) or jump on it and kill/march you.
I remember playing a role-playing game called Bushido, in where you could play a ninja. Once in a while, someone would play a ninja and it would be very disrupting for the rest of the troupe. Side meetings with the SG, use of skills a samurai would rarely take, yet everyone else in the troupe had to "ignore" some aspects of what was happening as it was a fellow player.
What he said.
This is the sort of situation where it helps to have the whole troupe have that play contract conversation....
Bushido? Not Legend of the 5 Rings?
Because it 'sounds' like something straight out of L5R!
An hermetic sorcerer can be very powerful IMO, much more so than a "normal" goeticist, since the substitution of Rego and Vim allows him to reach very high levels of power.
As I see it, this is a good thing, since it makes the infernal tempting, IF the GM keeps these infernal, corrupted and corrupting, and doesn't turn a blind eye to their use. If he doesn't, well, yes, it can be easily too much, at least as I see it (and I have seen it, over in Andorra...).
I also agree with JL that nothing good should come out of it, if only because demons will ensure it.
I think a lot of people above gave you a very good advice: By knowingly using powers he knows to be infernal, you are playing a bad guy, and this should have consequences.
Sadly, as Mouska quite accurately described, it seldom has, because, to not antagonize the player, the other characters and the SG will turn a blind eye to the infernalist's actions. And this is why I am not too happy when someone wants to use commanding/binding/ablating. Unless every player is really mature and ready to separate player/character and play out the consequences, it doesn't work very well.
A possibly good analogy IMO would be to perceive the character as something heinous, like a paedophile or such. Both for the player (so he understands he must really, really hide it and that no, this is bad) and for the other characters (so they can be revulsed and horrified and react accordingly).
The shortcut to power is very attractive.....this is good. However making sure that there are definite comebacks for the power is a must otherwise it goes from a good story to a fashion fad.
I would also start dropping clues to the other players early on. Hell likes strife and if it can get a zealous Flambeau to harvest the corrupt soul for it, and cause inter-order enmity then Hell wins on many levels.
A
No, it´s for PCs or NPCs.
I rather disagree that the "dark hero" concept can´t work. There´s nothing saying that consequences to his surroundings have to be realised or understood by the PC. 
It could also be a matter of different motives. The PC might be nudged into doing things, be they good or bad in the here and now, the effects of which in the long term are very different or simply part of a greater puzzle, where only the total pattern has any importance.
Or it could be that it is exactly the "the road to hell is paved with good intentions" and the PC is simply getting very slowly corrupted for one end reason or another, regardless that his actions may be doing great good now.
One way or another, something bad results from the actions, but the PC doesn´t have to be directly on the receiving end of the badness(ie allowing him to be that "dark hero"). But someone will be. And who knows what they might do? :mrgreen:
this is exactly what I suggested with the scenario of the rescued princess later committing suicide.