- "Carbon Dog becomes Diamond Dog after taking damage of several hundred HP. Now it's your turn to suffer. DD is hard. Use Multi-Bottle Rockets right away before it puts up its counter shield. Also use shield killer."
- — EarthBound Player's Guide
- "You think I'm down, you think you've won?! Boy I've got news for you: I ain't goin' anywhere! I'm best friend to neither man or girl, but I can diamondize all equally!"
- — Diamond Dog
The Diamond Dog is a boss in EarthBound, the second and final form of the Carbon Dog, and the final "Your Sanctuary" boss. This form of the Carbon Dog is stronger; however, its ability to breathe fire is now replaced with the ability to use powerful Diamondizing bites, which, as the name of the attack implies, has a strong chance of diamondizing party members. When this form is first activated, the Shield is also activated. The Diamond Dog is able to use PSI Flash along with standard biting attacks. It may also howl, which has no effect. Upon defeating the Diamond Dog, Ness gains entrance to the final Your Sanctuary location, Fire Spring.
The transition from Carbon Dog to Diamond Dog refers to the process of carbon becoming diamond through exposure to extreme heat and pressure. Diamond Dog's name may be a reference to the David Bowie album, Diamond Dogs, given all the other music references in the game.