Greyswandir is a mystery. Just what it and its companion sword [Werewindle]? are for and the extent of their powers are known only to Corwin and Brand.

Greyswandir was further empowered and altered by being carried by Corwin when he made his Pattern. It is extremely potent in Argent, capable of subtle and powerful Pattern manipulation. It now considers Corwin to be its God and busies itself with fulfilling his whims in Argent, even the ones he'd suppressed like his passion for his sister Deirdre.

Merlin and Fiona momentarily broke Greyswandir's connection to Corwin, making him aware of the sword's manipulations. Corwin threw Greyswandir away. Fiona has been studying it, carefully. Grey is emotionally distraught at being rejected by its God. Or at least that's what it seems like.