Mythic Blood gives a magus a single, non-ritual, hermetic power that can be invoked and dismissed at will (as if fast-casting) with no loss of fatigue. You get 30 levels, from which you must subtract any Penetration desired, and 10 and/or 5 additional levels if it can be invoked, respectively, without Voice and/or Gestures.
I often find myself unable to come up with powers that do not feel ultimately a waste, given what a magus could accomplish with just one more spell (perhaps mastered) or enchanted device. So, I am asking you: what choices have you found surprisingly effective in characters you've seen?
I guess that, to squeeze such a power for all it's worth, it should be something that:
a) does not need to penetrate
b) is useful in a fast-paced, tense situation
c) benefits from a ton of requisites
I think one particularly good choice would be the Seven League Stride - or perhaps a similar, instant transportation effect with shorter range but requiring no voice and/or gestures. Maybe some T:Group version of the Sling of Vilano to toss generic stuff around? Meh. Any other ideas?
I would add to your list:
d) the power should be something outside of the character's specialty. for instance do not choose transforming into an animal if the character is a muto Animal-corpus specialist.
Self-transformation. For example the power associated with the Hyperborean Descent variant of Mythic Blood transforms the person into a bird (swan or raven, choice at CharGen).
...how does the chosen spell interact with local Aura? I've only just thought about this, and I can't seem to find an answer. Not being impeded by otherwise hostile auras would be quite useful if it were true.
@lvgreen beat me, but any flight power is good. Invisibility also.
Otherwise, look at powers/effects from other tradition that cannot be easily duplicated by hermetic magic: fertility magic, or restoring fatigue level, rune-like effect (setting a sword ablaze without it becoming magical, thus blocked by parma).
I don't see why it wouldn't have the normal interaction: penetration modified by the aura. Yes, effects that you would really want in a difficult aura could work well. For example, Trust Me (perhaps at Diameter rather than Concentration) could be used with no voice/gestures in a strong Divine Aura, and you'd commonly want it in a Divine Aura anyway since so many people reside in Divine Auras.
Eh. Invisibility is relatively easy to cast with a formulaic spell for most people. Flight is a little harder, but not that hard. If you have a Deficiency with Perdo or similar, sure, something like invisibility makes sense. But you don't want to go with just generally useful if you can manage that with a formulaic spell easily enough. The Virtue is already one of the weakest Major Hermetic Virtues when you make a strong choice in the effect.
This would be a great idea if it were valid:
The effect should be designed as a Hermetic effect
I think it's a very reasonable house rule and make the power potentially much better.
It is designed as an Hermetic effect like most non-hermetic tradition are designed with hermetic-like effect (there is a base effect attached to arts, duration, range, target), but it does not say it has to follow magic theory limit.
Same way as creature powers and item effects. Since there is no casting roll to activate the power, there is no casting roll that can fail. Penetration will be adversly affected by foreign auras though.
that makes sense, and opens up new things for me to think about.
In that case I would go for
Perception of the conflicting Motives (InIM) 15
Useless against people with magic resistance, but no botch on casting in a dominion Aura (where most of the likely targets will reside) is not bad. But I assume someone who would want to cast this often would also like more mentem magics to be reliabel and subtle, so Deft Mentem and Qiuet Casting x2 would also be a viable choice.
I still think Seven league Stride is the best choice, or a "transform into a specific animal spell", when the player does not want to be in House Bjornear.