I just thought I'd mention that there is another ArM trope villain - the Diedne, returning to take vengeance on the Order. In this version, probably human-sacrificing pagan-god-worshiping zealots, perhaps driven to maleficia to escape the Order's wrath; just to make them a good, i.e. evil, enemy.
Other enemies include the Order of Odin in the north, or the Order of Suleiman (IIRC) in the East. Neither are too ominous or villainous, though.
Most of all, it is definitely the Church the Order fears. For good reasons.
But if we go back a bit, to the original post in this thread... I'm looking for a way to create a Voldemort-style NPC for my campaign. I haven't read the Harry Potter books, only seen the films released so far.
But if we stay with Hermetic Magic and the Order of Hermes, what kind of nasty virtues, flaws, spells and arts would be suitable?
The reason I want to use an NPC like Voldemort is that almost the entire group of players are new to Ars Magica, and they're all fans of Harry Potter.
One scene in the last Harry Potter movie (Order of the Phoenix) I really liked was the battle between Voldemort and Dumbledore, and the moment Voldemort possessed Harry Potter in some way (again, I haven't read the books). Something like this would be excellent for the NPC I'm making, the ability to possess people.
There is a Criamon Path that allows the practitioner to travel in spirit form (IIRC), and from there it's only a short distance to possession. However, this ain't quite it and you'd need to change the mechanics so I don't think it would be very useful.
A more useful idea, perhaps, would be the mystery of the Living Ghost [TMRE]. Basically, the villain turns himself into an undead ghost. He then can use magic to possess bodies - his, or others. The drawback is that if he's ever killed outside of his "haunt" (lair), he's dead for good; you can, instead, however, decide that only killing him in his haunt kills him for good (kinda like a vampire), or that only smashing his talisman (where he stores his spirit) kills him for good (kinda like a D&D lich's phylacntry), or so on.
As a side-note, a Living Ghost typically traps various spirits (genies, ghosts, and so on) in magical containers and slowly drains them of their power, using it to power Ritual effects or sustain spells. This is excruciating pain, the spirits are tortured into oblivion as their power is drawn forth. I think that could have it uses for a villain, especially if a PC character has Second Sight so could see/hear the spirits' wallowing in anguish (and maybe free them).
Another related possibility is that of dream magic [TMRE, again]. The villain could travel into people's dreams, and jump from one person's mind to another through the dreams. He'll manage to shape their dreams, and can build fortresses in their minds (imagination) and slowly reshape them. Imagine the villain corrupting people's minds until they live in a never-ending nightmare. He jumps from one nightmare to another with ease, and uses arcane connections to send nightmares to his enemies to both weaken them and allow him entry into their minds. A battle with him might take place in the mind of a person he barely touched, to ward him off; the PCs would enter the person's nightmare, and there face the (still partial, and weak) manifestation of the villain; if they fail to defeat him, the villain could overcome the person's mind and plunge him into a hellish existence, unable to discern between dream and reality and always at the villain's influence.
Another option is that of demonic possession. The rules in RoP:TI allow for a magus to summon and command demons, which do have powers of possession. The villain's minions could all be possessed. He would be trafficking with demons, and can use the rules to augment himself with various vile "gifts", including magic resistance and longevity, healing by draining demons (or angels...), and so on.
A cool power to give villains is improvements upon rituals. Hermetic Sacrifice [TMRE] allows the villain to sacrifice someone to power Ritual spells (instead of raw vis), and Hermetic Theurgy [TMRE again] allows him to summon and bargain with spirits, including powerful named spirits [Daimons] through lengthy Rituals. Long rituals are great things for the PCs to stop.
Magi would fear the nasty guy who is able to destroy their longevity potions so they would age or even die immediately.
If he is really nasty design a magus with extreme twilight effects. Althrough he is the member of the order but since his last return from twilight (he was away 13 years ) he is probably mad. Everybody knows he killed the former covenant leader and rule the rest but nobody is skilled or brave enough to attack him. Thats why they are afraid of marching him.
Some of his twilight scars cause very strong side effects so even his presence would be harming some way.
E.g. his aura can age everything in his presence quickly. Including people. And the parma doesnt protect against it.
You shouldn't give him overpowered hermetic effects because the players may get his lab notes or simply mimic his spells. He may have a focus using rare harming effects which form the magi rarely learn like Aq or He.
His weakest point can be the twilight and may has lower resistance against vim spells.
Hm. Voldemort is a tough one, as his magic as shown in the books and the movies is mostly Perdo Corpus and snakes, with a little mystery magic regarding his preservations and resurrection (although RoP:I tells you exactly how to do the "horcruxes" from the later books), but it's clear that he is able to do a lot more.
I would start by taking an aggressive magus (pick your House; I think there's room for any in this) and doing inordinately long character generation through age 120, including either mystery initiation or repeated hermetic breakthroughs. Make sure the magus gets all the necessary foci virtues, etc., and I'd suggest giving him at least the "Lesser Elixir" from Mysteries.
While I think Voldemort is a fair villain for people who are new to the game, my personal dream Enemy of the Order would be Thomas Aquinas as a super-powerful renegade Holy Magus. He'd of course have enough True Faith to bounce spells off of him, and he'd have the Church defending him from direct attack. Then he'd attack covenants both through the Church and with his incredible religious knowledge. He'd send letters via redcap with only the pronunciation of one of the many unsayable names of god, thus causing death, blindness, or insanity to all who read the letter and have insufficient True Faith.
I'm throwing another vote in for everyones favourite scottish badass Damhan-Allaidh.
My long running saga featuring him as the BBEG has just ended with his dramatic death, followed by the even more dramatic suicide of one of our senior magi to keep him dead. I had it that DA's armour acted as a kind of liches phylactery (or Horcrux in HP terms) and the armour was indestructible (meaning DA virtually was when wearing it). The only thing that could destroy the armour and make DA mortal again was if the wearer of the armour voluntarily commited suicide. So our heroic magi have a huge battle, kill DA and one of them dons the armour and stabs himself through the eye slot. Very noble.
I'm not sure if i read this somewhere or if i invented it but IMS DA could sacrifice a suitably prepared victim and turn their life force into a pawn of corpus vis. Using this method he became truly scary. He and his goons would sack a village, take 100 odd prisoners and BAM! a queen of corpus vis. Using that he could conduct terrifying rituals at range to murder opposing magi.
To emphasise what a badass he was in my saga, we had the players involved early in the disappearance of magi from several scottish covenants. DA basically drove the order out of the loch leglean tribunal before going on to sack Blackthorn and even kill off two of the english Archmagi, including the primus of house ex-misc.
When the Infernal book I came out I made a Summoner just to see what they'd be like.
If you want a powerful and versatile villain, make 100+ year old Summoner. Summoners can (with the proper summoning IIRC) get to huge ages without decrepitude and warping. They need to bind certain spirits (make them infernal of course) to do this. They can also summon small spirits and literally consu,e them for power, getting greater improvement than 30 per year. Finally, and possibly most importantly, they can bind a spirit or demon to themselves and get the spirit's Might as magic resistance. The greatest power of the Hermetics is magic resistance, they'll be awful surprised when their magic sheds like water off a duck's back when they try to blast this summoner (imagine him binding a 50 Infernal Might demon).
No rule bending needs to be done, just make an ancient summoner and you'll have your ultra powerful enemy non-Hermetic wizard. I'll see if I can find my post on him.
While the above suggestions are fine for what you are asking, I'll suggest that you might be asking for the wrong advice.
A great villain is a joy and a treasure for any saga. But with new players (of what level magi???), I'm not sure someone this powerful is reasonable to present as The Antagonist.
Instead of asking for someone so powerful he cannot be marched, how about someone so crafty that no one is convinced he needs to be marched? And instead of an Enemy of the Order, how about someone who will become one, only is not there quite yet?
This achieves several goals that are desirable:
It gives the PC's someone "their own size" (collectively) that they can struggle against, at least so they can survive without too much Deus ex Machina on your part.
It challenges the PC's to prove to others that he is as Evil as they say.
It means the BBEG cannot wipe them out with one flick of his hand - again, desirable, especially for believability.
Rather than trying to stop someone evil who is magnitudes bigger than they are, the PC's are trying to stop someone evil from successfully becoming magnitudes bigger, at least without anyone noticing.
From there, you can take the above ideas and back them way off, to a "Thulsa Doom, the early years" sort of level.
Or, take any political/territorial beast - a Tremere, a rogue Tytalus, even a Merenita with a bad attitude - and turn them loose.
To be faced with a huge lumbering thug that you have no "realistic" chance of defeating can be disheartening. If the PC's are to handle this on their own, without mentors and larger magi providing the sort of defenses and protections that, say, a Hogwarts can provide, you're going to have to balance the playing field.
Of course, my own preferred Enemy is not someone "bigger" than the PC's, but merely someone the same size but "better" - smarter, cleverer, better prepared. Nothing galls a Player more than having his Character get his ass handed to him by a peer.
) he is probably mad. Everybody knows he killed the former covenant leader and rule the rest but nobody is skilled or brave enough to attack him. Thats why they are afraid of marching him.