The HP Bar
The HP Bar is a formatting quirk used for appearances of particularly powerful signature Pokemon of particularly experienced Trainers.
Appearance
In its most common form, the HP Bar is a series of Full Block Elements (█) in a row, either in sets of 64 or 100, with color formatting around whatever section represents the owner's current amount of health. Usually it is aligned to the center of the page, rather than to the left. There are occasional variations, particularly in its first appearance during Jacob's fight against Pallad, in which it used forward slashes (////) instead of block elements.
It is unknown if the HP Bar actually has a physical appearance in-universe, although art of Pallad features it hovering over his head with the appearance of the bar based on how it looks in Pokemon Platinum.
Owners
Currently, the HP Bar is signature to Pallad.
Trivia
- Oddly, although Legendary Pokemon have strength and endurance that far surpass those of Pallad and any other potential owners (as demonstrated by Shadow Heatran, who defeated Pallad effortlessly), the HP Bar is never used for them.