To get a better handle on a character I'm working on, I've decided to try to stat out his heritage, ie. the doppleganger as a supernatural species.


The doppleganger is a supernatural creature known to temporarily assume the identity of mortals in order to carry out its nefarious ends with impunity.  They are the quintessential identity thieves.  While some monsters might kill, eat, or otherwise assault a mortal to 'steal' their identity, the doppleganger is far more insidious.  A few casual words with one is often enough for it to create a passable disguise.  Much more, and they'll begin to accomodate your various identifying mannerisms and even learned skills into their disguise, until even your most intimate acquaintances won't be able to tell the difference.
Dopplegangers are almost universally evil, frequently murderous, and predominantly of greater-than-human-average intelligence, though they vary from one individual to another as with any species.
They are almost never encountered in groups, but when they are, they are typically mate-pairs, and far more likely to resort to lethal forms of amusement.

Musts:
True Shapeshifting (with compels when necessary to forbid non-humanoid forms, but leaving the skill-shifting intact)
Modular Abilities: typical building block powers, creature features as appropriate (possibly Limitation to force the assumed powers to be suited to the assumed form)
Supernatural Sense granting the ability to see things for what they are (safer, but less potent version of the Sight)
some mind-reading capability; possibly Telepathy from the custom powers list, possibly just another Supernatural Sense

Minimum Refresh Cost: (9 or higher, depending on the telepathy option)
Options: additional Form Points; building block powers independent of Modular Abilities (and thus independant of the assumed form); Telepathy upgrades (if using that custome power)


Rejected powers:
Mimic Abilities: the incredibly circumstance-dependent potency of this power, combined with its unsuitable built-in Limitation make it less than ideal
Mimic Form: a similar built-in Limitation renders this similarly unsuitable
The Sight: I like to keep this potent ability reserved for Practitioners and 'higher beings' such as various angels with the ability to 'judge the worth of one's soul', but monstrous species spending most of their lives in forms other than their own, particularly in a world where other monstrous species might be doing the same, are bound to develop some sort of similar capability

Ideas?  Comments?  Suggestions?

So I've got a character bouncing around in my head that's been demanding a bit of leeway from the usual rules in order to be properly represented, so I figured I'd pass some of those altered rules by the folks here to get your opinions on how they might (or might not) adversely affect game balance.

the character:
a young, somewhat underachieving, (apprentice) wizard prodigy who takes Dresden's 'without my foci, it would just be too dangerous' schtick to an extreme (actually having an aspect being called, for the moment, 'without my foci, I'd kill us ALL')

I've modeled this, mechanically, by giving him full Thaumaturgy, and several Refinements, but neither Evocation nor even Channeling, then devoting substantial specialization and focus slots to Crafting, while flavouring those items as incredibly dedicated 'foci' for his 'evocation' spells, including his 'potion' slots, which I've flavoured as foci that 'burn out' after just one or two uses

To aid the consistency of these items being foci for evocation, and not actually storing spell energy themselves, though, I've performed a bit of a reverse of one of the usual enchanted item options.  Instead of reducing the power to increase the frequency, I've dropped the frequency to 0 - instead relying on that oft-forgotten option to pay mental stress to gain extra uses of items - increasing the power by a commensurate amount.

So...that's the biggest workaround that this character would be using.

Beyond that, I'd been intending to invoke-for-effect 'without my foci...', probably while simultaneously handing the gm a pre-approved compel, to lay down the occasional mostly-indiscriminate destruction in the style of zone-wide evocation attacks.
I'm not quite set on the details of how to implement this one, though, beyond the base concept, but even Channeling seemed to expensive for what I had in mind (basically a single spell effect at significant cost of collateral damage, without justification even for having an enchanted item 'focus')

Is it just me, or is 'Victor Sells' Heart-Exploding Spell' (YS301) estimate of the shifts necessary to fill a stress track significantly more than would be indicated by the stress rules on YS202?
'Heart-Exploding Spell': "...plus 10 shifts to fill up a
strong physical stress track (4+3+2+1)..."
YS202: "When your character takes stress, mark off
that box (and only that box) on the appropriate
stress track."  (bolding added, italics original)

Which, at that point, would be the TENTH stress box, not the fourth, third, second, and first, combined.  And since the target, assumedly, does not have ten stress boxes, they're going to be good and taken out.  By a rather significant margin.