The Rock of Destiny is the only weapon Puppysmiles carries with her throughout her journey -- excluding the EMP Tank Shell & Henrietta's pistol. The rock was named by Puppysmiles' Mark VI suit and became her primary weapon. Puppysmiles uses the weapon on multiple occasions, using it to take down opponents that would normally require a lot more effort to kill.
Puppysmiles threw away the Rock at the end of her journey, when she discovered her mother, Rainy Days', grave marker. The rock landed on a metal chest on the beach behind her mother's gravemarker and was used by Henrietta Firebright to break open the lock on the same chest.
The Rock of Destiny was last seen as the final stone on a small stone cairn built near Rainy Days' grave in memory of Puppysmiles.
