Overview:
The vizard are shinigami who have obtained hollow powers and whose shinigami powers remain dominant (although they do have to undergo a process and maintain their dominance over their hollow), while the arrancar are hollows that have obtained shinigami powers and whose hollow powers remain dominant. Having begun as shinigami, the vizard appear entirely human. Unlike the arrancar, they do not have holes or partial masks (common traits of transformed hollows) anywhere on their body, though they can produce masks on demand, and they carry zanpakutō like normal shinigami. When using their hollow powers, a vizard's appearance does not change except for the mask on their face and the color of their eyes, with the whites of their eyes turning black and the irises gold. This process of donning one's hollow mask is referred to as Hollowification.
Abilities:
In battle, the vizard use their hollow powers to augment their shinigami abilities, granting them massive increases in speed, stamina, and strength. They also gain access to some of the common hollow abilities, such as cero blasts. Bodily harm can seemingly be ignored while wearing their masks, as demonstrated by Ichigo's hollow during his unwilling transformations.
Vizard zanpakutō seem to function in the same manner as those of standard shinigami; however, none of them have explicitly used their releases in combat yet, excluding Ichigo and Kensei. The vizard seem to prefer their mask-given powers to their shinigami abilities. The vizard remain in complete control while wearing their masks, unlike Ichigo's early unstable transformations. While this transformation seems to have a time limit initially, more experienced members are apparently able to maintain their hollow forms indefinitely, or at least for periods of such length that the time limit is a moot point in battle. As suggested by Aizen, the fusion of the two spiritual entities allows these shinigami to reach levels of power far surpassing that of either side.
