Hatched Pokemon will always be of the mother's Pokemon type...
...except when breeding with a Ditto.
- If Greninja is female and Feraligatr is male, then you will always hatch Froakies
- Greninja is male and Feraligatr is female, then you will get Totodiles
- If they are both the same gender (both male or both female) then they will be unable to breed.
If you are breeding a Pokemon with Ditto, then the gender does not matter - even some Genderless Pokemon (like Magnemite) can be bred with Ditto.
Another thing to keep in mind is that Pokemon are grouped into compatible breeding pools, known as 'Egg groups'. Luckily, both Greninja and Feraligatr are in the Water 1 Egg Group, which means they are compatible.