The platinum shovel doesn't work any better than the onyx shovel, but you'll feel much snazzier wielding it.
How to Obtain
Make an onyx shovel. Then go to space biomes and search for platinum. Lots and lots of platinum. When you have enough, craft it. Can also be traded for.
How to Use
Wave it around to frighten crows and to cause envy and jealousy in your fellow players.