In the Beastiary, 3rd printing, it states that the Derro has 3d8+12 hps. The +12 seemed strange to me so I looked up the Derro in my D&D 3.5 Monster edition and it shows the hit points at 3d8+3. I don't think I've ever seen the + a higher number than the die so I'm wondering if this is an error or if there was some reason for raising it to +12?
The bonus hitpoints are derived from constitution, the derro seems to have 3HD and 18 constitution in Pathfinder..
I think it changed to make the derro a suitable CR 3 opponent in relation to it's other abilities.
It has indeed!
If you read its race's history over at the PF wiki you might even get an ingame explanation.
Ruyan.
To me, their history indicates that they're a hardy race, having to endure hardship and constantly fighting for survival after the Vault Keepers vanished.
Maybe it's just me. *shrugs*
Ruyan.