At the end, the egg hatches. It's a duckling. Marlene brings Mother Duck to the boys to get her duckling back.
Unfortunately, the effects of the Penguins' training goes to a point where Momma Duck asks the Penguins to do something to stop him (see Hard Boiled Eggy). Their attempts to show Eggy the dangerous portion of their missions fails, as the duckling goes on a rampage taking down all the animals in the zoo, Eggy inherits 5 traits.