This is the 8060th most frequent Polish word.
nietoperzowego
"Nietoperzowego" means "bat-related" or "pertaining to bats" in English.
The word 'nietoperzowego' is used here as an adjective describing the style of flight as resembling that of a bat.
Nietoperzowego stylu lotu nie można zignorować.
The bat-like style of flight cannot be ignored.
Here, 'nietoperzowego' describes the shape of the mask as similar to that of a bat.
Podczas balu nosił maskę nietoperzowego kształtu.
During the ball, he wore a mask in the shape of a bat.
In this instance, 'nietoperzowego' characterizes the atmosphere of the scene as reminiscent of bats or their associated environment.