HP Plus (Super Paper Mario)
From the Super Mario Wiki
The HP Plus is an item appearing in Super Paper Mario. Similar to the badge of the same name, it increases Mario's max HP by 5. However, unlike the badge, its effects are permanent. It is found by using Cudge to uncover a hidden switch near the Flopside Pit of 100 Trials, then going to the parrallel area near the Flipside Pit of 100 Trials and opening the big treasure chest there.
Additionals can be purchased from the Flipside Arcade for 2500 points.