When you collect a HP patch, it increases your HP bar. HP is a rarer patch, and you can only collect 16.
A single HP Patch is a character. He hates the kirbies and does not like to be collected, similar to the Shadow Star and All Patch. He does not like hiding on the UFO, instead, he decides to fight the kirbies with all his weapons. He usually goes to hard to reach places, such as the Star Pole, the Electric Lounge, and, despite what I said before, the UFO. (He's not hiding, he's trying not to be reached when trying to defeat the kirbies. He's actually just blowing the cover of all the other hiders.)