After years of trying I have finally swayed my usual gaming group to start an ArsMagica saga.
This being 2009, I thought we'd embrace the 21st century and play the 5th edition so I bought the 5th Ed Core book and have been busy foraging into my old RPG books library. I unearthed a number of old volumes from 2nd and 3rd edition with the intention of using them to flesh out my stories.
During a mock-up combat, I quickly realised that some key combat stats had been seriously altered in the later editions (I don't know if this came in 5th or 4thEd). Soak and Damage in particular have been so much lowered that four (young) 5th Ed characters will have no chance to even cause a single wound to a mundane 2nd Ed Bear.
So, I checked the Bear stats in the 5th Ed Bestiary and found that indeed it had a considerably lower Soak than in the 2nEd (10 vs 25).
Unfortnately, comparing a few other beasts didn't seem to imply a simple rule for converting the stats.
So, how are you, ArsMagica Journeymen and Masters, converting older editions key stats to the 5th Edition?
The problem I face is of course not so much for mundane beasts, but all the antagonists described in old materials (The Tempest, Tales of a dark age, sorcerer's slave, etc) which I'll want to include in my Saga without unbalancing the game.
Unfortunately, there's no quick and easy way to convert stats across from older editions. The bear was an unlucky choice; its Soak was too high (relatively) even in 2nd edition, so it was deliberately cut. For combat, in particular, there were a lot of small changes to weapon statistics and to rules to get rid of various anomalies, such as the whip being the most deadly weapon in Mythic Europe, and armour increasing the severity of your wounds.
The easiest way to convert is to buy lots of ArM5 books (Broken Covenant of Calebais would be very useful) and just steal the most appropriate looking statistics. The Realms of Power books have lots of creature stats.
As for magi, I'm afraid there's really no easy way to convert. Not only have the numbers changed, but what the numbers mean has also changed as the guidelines have been altered. If you want to play strictly by the rules, you'll have to do a lot of work to convert things. If you're willing to fudge things, though, the old books are still great sources of inspiration.
I think the best way to convert is just to eyeball it and take your best shot. Ask yourself questions like "how many years did this character spend working on perdo magics?" or "how hard of a hit should it take to cause a light wound to this dragon?" and then work backwards to get your numbers. Creating a system of conversion rules is going to provide you with more work and inferior results.
You may have to do it from scratch. Basing it on characteristics (keep the same, it won't matter much), abilities (possibly increase, 5th is easier for focusing xp on combat), and weapon/armour used.
The book of mundane beasts probably covers most creatures the pc's would likely fight with, though changes may alter how the adventure author expected things to go.
Non-mundane creatures, re-create the creature to suit your players.
I wasn't so much worried about the Magi: if the characters were to meet a Magus and need his combat stats, then this would be one of the highlights of the story and therefore these would focus my attention.
Instead I was more worried about the inconspicuous 2nd rate "encounter" which, as the Bear example proved, could turn very ugly.
I guess, I'll simply have to practice a lot and be ready to change things behind the scenes if I sense the characters somewhat cornered.
@Erik and DireWolf, Yes I meant the book of beast (ArM5Beasts.pdf)