The Porcupine is a character introduced only during Bambi II.
He's impatient, easilly upsed and very territorial, he will do everything to protect his home, a fallen trunk, the only bridge to cross a small river. When Bambi tries to cross it, he gets to see how dangerous the porcupine can be. Bambi "uses" him against one of the hunting dogs that, near the end of the movie, was chasing him. It's thanks to the Porcupine that, at the end of the movie, Bambi kisses Faline.