SOLVED. Fantasy-Boy is turned into mouse or rat, wears skull as hat/helmet. [s]

[Jared]

I saw this book (series) in a store circa 2009-2010 but never actually read it. Covers depicted rat or mouse characters, one of whom wore a skull of some kind as a hat or helmet and carried a sword (may have been a needle or something). Looked at the summaries, which indicated that the skull-wearer was a human boy magically transformed into a rat or mouse. One of the character was a female rat or mouse with magical powers. She was apparently responsible for his transformations and also could transform herself into a human.

Plot summary described rats/mice fighting against some threat; can't remember the specifics.

[Ayshe]

Of Mice and Magic maybe?

[Jared]

That's the one! Thank you!