Your ability works by intuitively analyzing and understanding a creature's reality matrix, and your memory isn't infinite. So you must interact with a creature for at least five minutes before you can take its shape, and you generally can't shift into forms that you last took too long ago: your memory for matrices only goes back a few months.
You cannot shift into non-living forms: the form you take must be living and organic. That aside, you can shift regardless of issues of size -- you take on forms as small as a mouse, or as large as a large Construct, with equal ease.
To shift into the form of a character in the game, see a GM to get the appropriate button. To shift into another form, talk to a GM about whether it is reasonable. You may shift for free once every half-hour; to do so more frequently than that, you must spend one Point.
Characters In Game: Sarah
All Characters: Sarah
The following are notes made while this was in development. They do not necessarily represent the current state of this ability.
Sarah may shape-shift into other creatures, with certain limitations. She can only shape-shift into people or beasts that she has seen physically for long enough to see their form clearly: to imitate someone, she must have interacted with them for at least five minutes. She can not shift into non-living forms. She can shape-shift regardless of size -- shifting into something as large as Fust or as small as Artie are equally easy. She may shape-shift freely every half-hour: doing so more frequently than that costs her one point.
Her shape-shifting is reality-based, and is quite complete: she takes the form of who or what she shifts into, right down to the smell.