If a magus casts a spell with range Touch on himself, it must penetrate his own magic resistance.
What’s the real-world game-design rationale for this position? How would the game break if magic resistance didn’t apply here?
Note that I’m not after the in-universe answer that the magus would give.
That only applies if the magus doesn't know Parma Magica. If a magus do know it, he can lower both his Parma and his Form Resistance.
Why this design ? I believe it's because, if a magus of Hermes confronts another magus who doesn't have Parma, he would at least have some protection from magic.
Why 2 different resist ? Well, in terms of game design, that would just mean Magus of Hermes are just really difficult (or almost impossible) to confront with magic. Magic is their domain and they master it. Now was it really necessary ? I don't think so. Apart from Certamen and House Rules, magic fights are just some mini-spells you throw at your foes (except if you are a God in this domain).
Small Example : 7 in Ignem and 3 in Parma means at least 23 Penetration (7ig+15parm+1minimum pene against 0). And you're not even that good in either of them.
Now the game would only break if you confront a non-Hermes Hermetic magus. Because they would be so weak against a Pilum of Fire which is the basic of basics attack spell. But if you don't intend to throw this kind of encounter, that would just means don't confront mage with spells.
Oh. It still applies. Lowering PM to cast a spell on yourself is non-trivial. You’re talking about spending the time to lower PM and then making an EF 12 Concentration check, assuming nothing else is distracting you at all.
It wouldn’t break the game, but it would make some things much easier for magi and make you need to consider some other scenarios. That Personal spell you have to go under your PM and that Touch spell you have to help your friends can now just be the one Touch spell, for instance. And then there is the question of someone occupying your space incorporeally if we’re saying internal Touch bypasses PM. Should a ghost get to bypass your PM if internal Touch bypasses PM? These can all be handled, just things to consider, and thus why it’s not game-breaking.
That.
I think it's a nice touch and feels consistent, and encouraged magi to develop spells that affect themselves which is nice gamewise (even if the official spells sometimes don't make use of that - like invisibility).
Oh, and callen - glad to hear from you, been a while.
Thanks for the insights, folks. It seems like there’s no huge consequence I’ve missed, but it adds nice flavour to the game. Sounds good!