Wizards are the decorative motif of Rose's Mom, analogous to John's Dad's harlequin motif. She has covered her whole home, except for Rose's bedroom, with these fantasmical finger-wigglers. They seem to be primarily European wizards, sporting long flowing beards of unfathomable wisdom and cavorting with unicorns and dragons in a Merlin-esque manner. Rose is under the impression that her Mother hates these wizards even more than she does and she only collects them to spite her, but indicates that Dave disagrees. This is one of the many actions that Rose has mistaken for passive-aggressive antagonism (see, for instance, Jaspers' Mausoleum).
In actuality (and unlike John's dad, who collected harlequins purely to bond with his son), Rose's ectobiological mother was likely every bit as obsessed with wizards as her collection indicates, at least going by her. At the very least she seemed to collect them in order to be closer to her daughter who was interested in magic, albeit a different kind.
A twenty foot tall granite wizard, Zazzerpan the Learned stands majestically within Rose's living room as the most extravagant example of this theme so far. Zazzerpan, however, is destroyed while Rose struggles to enter The Medium.
Wizards are known to possess magical properties. Combining a wizard statue with another object via alchemy creates a magical version of the object. This property is used to create the Needlewands. Later revelations in the story cast doubt on this though as the two users of "magic" had other power sources granting them their abilities.
Roxy Lalonde has wizard dolls in her bedroom. They look the same as the ones in the lab under Rose's house.