Updated.
Ready for the dire version?
It needs the standard Climb skill text:
Skills: Porcupines have a +8 racial bonus on Climb checks and can always choose to take 10 on Climb checks, even if rushed or threatened.
The biggest species of Porcupine can reach 40-60 pounds, so I wondered about making the Advancement 1 HD (Medium)
or 1 HD (Small); 2 HD (Medium), but I'm not sure I'm that keen on the idea.
Oh heck, it's just on the cusp of Small/Medium, so we might as well leave them Small.
Porcupines have a couple of other curious traits, such as:
Porcupines have excellent spatial memories (to remember were food-trees are in forests) so are good at navigating mazes and the like.
The North American Porcupine (
Erethizon dorsatum) has antibiotic skin, so it doesn't get infected if it falls out of a tree and wounds itself with its own quills.
However, interesting as that is I think we can safely leave them out. (If the wizards left the tremorsense out of Crocodiles we can leave the navigation sense out of Porcupines).
Basically, this is a long way of saying "Give them the Skills writeup for Climb and move on the the Dire Porcupine".