This egg was only available in Egg Cave's Cash Shop Park for September 2013.
Oos eggs are not actually true eggs. Instead the young Oos grows tadpole-like within a thin membrane. Nests of Oos eggs can be found in rock spires at the bottom of Ark Bay, where they are vigilantly guarded by the father.
Young Oos rarely leave the rocks that form Oos nests, until their fins develop more they are rather clumsy swimmers and make easy prey for other ocean dwellers. As they grow they become more and more graceful and swift swimmers. There is very little that can catch an Oos once it decides to swim away. Oos also secrete a mild toxin that they store in the spines on their tail. This toxin creates a disorientating effect that is used to confuse both predator and prey.