So I'm getting involved in a game of Ars Magica for real after 6 years of failed half attempts. We're making characters an I had some ideas to bounce around with people who might have more of an understanding.
So I was plugging along character creation making a Gifted Mercere who focused on Rego Auram and Rego Corpus. My idea was one that could teleport and control the weather. Seemed like it fit with the 'traveling/messenger' line House Mercere tows. But then I see that House Mercere get Puissant Creo or Puissant Muto for free. The mental gears come to a halt. Not so much because I want to go back and min/max or cram my character idea to take advantage of this free bonus. But more because it throws my understanding of House Mercere for a loop. Ok so House Flambbeau gets Puissant Ignem or Rego. That fits the 'stereotype'. I get House Bonisagus getting Puissant Magic Theory or Intrigue. But what's with a bunch of messengers receiving bonuses to 'I Create' and 'I Change'? So... they like to turn into animals? That seems like a Bjornaer thing. They're healers? Ok, that's cool. I guess that sort of helps people get messages from point A to point B...
So what's the deal with that? Could someone explain House Mercere to me in more detail?
If I recall correctly, Mercere himself (herself?) was an expert in Muto magics, so the focus. The Gifted magi of house mercere are the Mutantes, a line of magi with certain control over the parameters of their spells. There are few of them (less than a dozen) and they do most stuff "at home" since they have an automatic appointment as "providers of magical trinkets and longevity rituals for the rest of the House". Revealing against that system is fairly difficult. Not much travel for your Mercere according to canon. However, feel free to do as you please. I have had Bjornaers defend a forest being razed and Tremeres being the good guys, so hey.
The concept of your magus is cool. it can fit in any house, acrtually, not only merceres. it would make a great Trianoma or seeker, for example.
Basically, Redcaps, i.e. Mercere messengers, are ungifted members of the House; they can be members of the Order without being magi exactly because they serve as messengers. To make one, you do not use your magus character, but instead make a companion with the Major "Redcap" virtue. You do get 50 levels worth of magical items at the start of the game, which you could tailor to your "move around" and "control the weather" goal. If you provide good service, you get extra items, at an average of +2 levels of items/year, and a longevity potion when you start aging (this is all in the corebook).
Gifted Mercere are an entirely different thing. They are a minority - perhaps only 10-15% of all Merceres are Gifted. They do not deliver messages, except occasionally for sport They are much more your "standard" magus type. Mercere the Founder was a Muto specialist, and his lineage maintains the tradition - these are the ones with the Puissant Muto. Also, many Gifted Mercere are longevity specialists responsible for creating the longevity rituals of the ungifted members; since longevity specialists obviously concentrate on Creo and Corpus, the Arts to make longevity rituals, this explains the Puissant Creo.
I suppose me disconnect is how the Gift Mercere magi apply their limited abilities (because of their numbers, or lack there of) to the task of the house which they belong to. In my mind, I would peg them as wanting to help their Redcap brethren be able to 'deliver the mail' timely and with care. So clearing the weather for a messenger to get through... healing a tired beast (or outright summoning a new one) for a redcap to continue riding... enchanting redcaps with the ability to see at night so they can travel longer... changing the winds while at sea to make good time... all the way up to flat out instant teleportation. Not so much "make the best longevity potions", ya know?
Apparently the policy of the House is to equip unGifted members with magical items, so they are more independent. Since the House is rich, it just puts out lucrative contracts for would-be-magic-crafters (this is from Houses of Hermes: True Lineages), many of which are snatched up by Verditius magi. It does make sense to me...