A player asked if he could take a Mental Construct lab as a virtue.
I must admit I answered "er.. can I get back to you on that?"
So what sayeth the mighty Ars Magica Hivemind
What do you think?
Impossible? Minor Virtue? Major?
What is the benefit of such a semi-disfunctional lab?
If a character spends a season somewhere she'll want to be in a defendable sanctum anyway. The character will need a room and a lab that can do items ánd familiars anyway.
I consider such a lab an elegant extravagance - and a rather harmless one. So minor virtue.
BUT there are a few questions that you should decide upon:
- does using the lab cause warping?
- are lab texts produced (there is a minor virtue for magi who do not want to write down their lab texts)?
- is it an item or the result of a spell/magic accident etc?
In terms of "raw power" I'd say it's a minor virtue in most sagas; that's because most magi get "for free" a better lab. Sure, a mental construct is easier to carry around, but I do not see it as such a huge boon. Of course, in a saga where magi are renegades constantly on the run it may be worth more...
Really depends on the game and the player. I mean, it's a big source of Inspiration for Dream magic......
Depending on who it´s for it can be a minor virtue, a minor flaw(lab not useful for everything and also cause warping) or a free virtue.
Actually i´d say, go for houserules on how it works, i was never satisfied with how it was written, especially the added warping makes it more annoying than good in my view.
Mental Construct labs are certainly potentially possible in setting - "Mental Construct" is a Major Supernatural flaw for a lab (see page 120 of Covenants).
The text of the flaw suggests that one way to create such a lab is a powerful CrMe ritual (which I'm guessing would be a momentary ritual, which wouldmean you didn't get warping for being under an ongoing effect (although might for a powerful effect, depending on whether it was designed for you or not). It's also quite restricted in what you can do in it, but there are limits on what you can do in it - basically, inventing spells is in, working on items or people is out. There's a bit more - see Covenants for the full statistics.
I'm aware of the lab-flaw you mention - it inspired the question in question... was I insufficiently clear on this?
My player wanted it inately and without warping - mostly for style I imagine.
Since you mention it, yes I imagine so!
The player war explicitly asking for a version that does not cause warping. If it does cause warping the whole discussion is academic at best 
Good point. I haden't even thought about that.
Still undecided - this is for a "hmmm, maybe I should have an extra magus in case I'd need another character", rather hypothetcal at the moment.
If he doesn't want Warping, Then what does he expect to do in his "lab"? if it's just researching spells and reading, then make him learn "The Art of Memory", and as a minor virtue, let him do that little extra. His "lab" is really just flavor text at that point. More than that, then Major Hermetic virtue, and a "free" hidden enemy flaw, from those in the Order suppressing Dream Magic.
Read the last part of the Flaw, the LAB gets a warping score added to it. Even if zero other additions of warping is added, a mental construct lab will produce either a sideeffect or a modified effect 20% of the time. It doesn´t sound much but it gets annoying really fast.
A houserule i think is decent is allowing a lab to reduce Safety points to remove Warping points, usually at a 2 for 1 rate, making it rather "expensive", but still letting you get away with the options causing warping.
My question is how did the character acquire this lab? What magic created it and sustains it.
Ths was not specified, but I think the idea was innate - where does your Tough virtue come from, what magic sustains it?
Well my Tough virtue comes from and is sustained by Ibuprofen. 
My Mythic Intelligence however is powered by my humility. Can't understand why it's not more reliable. 
I was actually curious if it was explained as some sort of magical effect like the crown of hemes, a "natural" mental talent that works along the lines of the art of memory or just a wondrous and unexplained product of a magical world.
Strictly by the rules an inherent magical effect is doable as the Personal Power minor supernatural virtue from RoP:M. Although you'd need two minor virtues to get near the level of effect required. Since you can potentially step outside of hermetic limits with those virtues the effect might not even warp the character.
Or if the character's in your saga normally are allowed to use the customized lab rules as starting characters then a virtue is unnecessary. As long as the character is okay with it as there primary lab or can finagle two labs.
I think this was the intention but I'd have to ask 
It would be a great Mystery virtue for a new path, which would permit the virtue without the warping.
I'd say let him have it. Story integration is more important than magic integration - so if it fits in with his overall character concept, fantastic. Virtues like this are easily explained by Esoteric Mysteries - the exploration of which is great for story and the integration of them is a good focus for Hermetic research.
Make him take the Mysteries ability Memory : 3, minimum. Perhaps have his Memory ability act as a stand-in for Magic-Theory for lab-refinement (which is a substantial flaw in and of itself - necessitating an extra ability which would be a huge xp sink.)
Perhaps pitch to the player that this is something he can take if he wishes to be part of a Mystery story-line - which could open up some interesting Story, Personality or Supernatural flaws which could empower the lab.
Some examples might be:
Weekly or daily meditations necessary to maintain the lab.
Flaw dutybound : Cult, or Weak magic resistance : Cult leaders (as with Secret Name Bjornaer virtue) or Visions
If you really want to have fun with it, you can give him a Flaw/Virtue of Amnesia : Cult membership. He could be a sleeper agent for a cult with powerful mentem magic (perhaps the dream magic cult whose name now eludes me) whose memories of the cult have been wiped clean. He acts in their interests without knowing it, as they secretly manipulate his memories and personality. 
The flip side of this is that he has the ability to initiate (or even spontaneously rediscover) comparable virtues like Dream Magic or Inscription of the Soul, or have useful "flashback" style insights to mysterious happenings in the game.