That's a clever thought!
Question, though: if you have a pre-done spell (e.g. in a potion, an item, etc) that is a shapeshift (bypasses the (physical) Stress Track and (for example) turns you into a bird); and someone else uses it (who can)... It turns THEM into said critter, instead. Right?
But what if they have some sort of Toughness, and their stress-track is bigger?
Honestly, it doesn't make much sense that "physically tough" = "resists fixed spells that cause an all-or-nothing effect".
I'm almost inclined to say that this should be "enough shifts to bypass a normal human's Stress Track & cause a Consequence" and then it works (even when they have Toughness).
But I'm not at all sure of this... someone would game the HELL outta this for combat-items. Maybe add a "willing target" clause...?
<wanders off pondering>
If you are using potions to shapeshift into a bird then, instead of buying a point of refinement to get more potions, spend it on diminuitive size.
A potion that can transform another person requires lots of shifts. 5 shifts + 1FP or +3 shifts/refresh.
So, you need to brew an 8 shift potion that grants diminuitive size for one scene.
Or you give them a 5 shift potion and they have to spend a FP to boost it.
Honestly, I never thought about it too much. Buying a toughness power for 1 scene costs 11 shifts.
Lore 5 + 6 shifts invested through refinements, specialties or Enchanted item slots.
That's a huge resource sink into potions just for one use. And they only recharge 1/scenario.
But what if they have some sort of Toughness, and their stress-track is bigger?
Honestly, it doesn't make much sense that "physically tough" = "resists fixed spells that cause an all-or-nothing effect".
Well, these aren't 'all or nothing' spells. If I cast a 6 shifts spell against an enemy, a tougher opponent will be able to soak more damage. The spell doesn't really know the difference between friend or foe. If you take meds, they're usually dosed based on your weight/size etc...a 300lb person won't be affected the same way as a 120lb person if they're given the same drug.
Just my opinion. I'm sure this has all been discussed before. If I get around to it, I'll post the thread.
Maybe add a "willing target" clause...?
The only mechanic you have to make it easier is to choose not to resist. This is why it's 5 shifts. a 4 shift stress track needs 5 shifts of energy to bypass...unless they resist. In which case, to be safe, you should pump in 9 shifts (in case they roll a +4 on the dice). Not to mention that, if their stress track is 0000, it means they have an endurance of +4. So, you need to an additional 4 shifts for a total of 13. Just to be sure you automatically taken them out...