From the Super Mario Wiki, the Mario encyclopedia
An Angry Spear-Mask can be created by Ground Pounding when there is a nearby Tornado Spear-Mask (that isn't stunned). If Wario Ground Pounds and there are Angry Spear-Masks in range, they will transform into plain Spear-Masks. They're much like the Tornado Spear-Mask, spinning their spears when they turn around. Upon spotting Wario, Angry Spear-Masks raise their spears in the air and charge towards Wario; during this time, Wario can jump over and attack from behind, as they do not turn around.
Angry Spear-Masks are extremely rare to find on Normal difficulty (in fact, the only set Angry Spear-Mask that is encountered is in Monsoon Jungle). On higher difficulties, they begin to appear more frequently. During Super Hard Mode, all regular Spear-Masks are replaced with Angry Spear-Masks.