Crocoducks is a curious combination of chickens and crocodiles. They are an inherently vicious creature prone to attacking anything and everything except for chickens. Ocelots, however, will actually attack Crocoducks so you can use them as a tactic for obtaining their eggs.
You can breed a crocoduckling by getting two adults together and feeding them raw meat. A duckling will hatch and you can use raw meat again to tame it. It will then follow you around forever.
The duckling will take a day or so to grow into adulthood and then it will start attacking anything in its path, except for you. This is great to have when it comes to enemy mobs, but also be aware that it will attack your other tamed animals so be sure to keep the two separated. You can even use leads to guide your duck away when need be.