cosmic spirit
Assist helper guide from Super Mario Galaxy 2. Appears if the player loses too many lives in a level. Accepting her help will have her enact the Cosmic Guide mode, which takes control away from the player and guides them to the Power Star.
Bears an extremely close resemblance to Rosalina, having the exact same body and silhouette but instead is covered entirely in dark blue/black coloring and starry sky patterns while lacking eyes. Whether they are the same individual or if there's any other connection between them is unknown.
Called the Helper Witch (おたすけウィッチ) in Japan.