Shapeshifting

Maggie Finson wrote this article in Questions and Answers: Power Categories except as otherwise noted.

Shifters have a powerful psychokinetic ability over their bodies at the very molecular level. There is some connection between the shifter syndrome and the exemplar syndrome, but shifters very rarely display exemplar traits.

Shifter classification codes, based on effect:

code	meaning	explanation
u	unstable shifts	body(part) reverts from shift to some natural form
t	toggle shift	a set number of forms exist and the body shifts back and forth between them
i	one-way shift	each shift ends with a new 'final' product that is stable

code	meaning	explanation
f	full form shift	no partial changes possible, form moves from one complete to the next
p	partial form	capable of shifting a limb, skin, or any major part of the form
r	refined	capable of shifting a very refined portion of the form

code	meaning	explanation
a	appearance	shift is appearance only, the actual make-up of the person remains same
n	functional	internal organs and body chemistry adapt to serve new form
c	complete	the new form is completely unique from the previous, and fully functional in any way (only type c of the a/n/c grouping mimics powers and innate talents)

code	meaning	explanation
s	stimulus	shift is triggered by an external stimuli
w	controlled	shift is controlled through willpower or some directed means

code	meaning	explanation
m	mass constant	mass remains constant during shift
l	localized	mass varies within a limited range using external objects to comprise difference
e	extended	mass varies within a limited range, not taken from an outside source
g	irregular	mass fluctuates from form to form without limit

Overall Rating

Level 1	limited to first stage (u, f, a, s, m) in at least four of the following: number of forms amount of body that can be changed functionality control mass limitation (and not meeting req's of 4+).
Level 2	limited by at least three categories as above (and not meeting req's of 4+).
Level 3	limited by at least two categories as above (and not meeting req's of 4+).
Level 4	minimal rating for a shifter showing at least one of the classifications i, r, or l
Level 5	minimal rating for a shifter showing at least one of e or c, or showing both i and r
Level 6	minimal rating for a shifter showing classification g, or showing all three of i, r and c. Can ignore the laws of reality when he shifts.
Level 7	Can shift into inorganic substances.

Finally, if a shifter can shift to gain powers in another category (for example, if they can shift to become as strong as a level 4 TK, or duplicate the feats of a level 3 exemplar), then they are given at least that level in shifting power.

Note - take the rating section with a large grain of salt. It doesn't match the general rules for ratings, and sometimes it gives an absurd result.