Hit Points or HP is how much damage a monster can take before being Knocked out. Once a monsters HP hits 0 it can no longer fight until it has been healed with a healing barcode.
A monsters HP reads X/Y with Y being the maximum possible Hit points and X being current hit points.
Potion(+20), Potion(+10), and using a healing barcode are the only ways to recover HP.
note: Potions can only be used in battle.
When a battle is won each monster on the team, even when knocked out, gains one maximum HP. This does not increase their current hit points so even if a monster does not take damage it will still need to be healed 1 HP after battle.
The maximum possible HP for any monster is 99, if a monster goes into a battle with 99 HP and wins it will not gain the +1 HP bonus.
Experience points do not control level up as would be expected, instead monsters go from level 1 to 2 when they reach 31 HP and from level 2 to 3 when they reach 70 HP.