Feraligatr's BST is 530 and its stats are 085 in HP, 105 in Attack, 100 in Defense, 079 in Special Attack, 083 in Special Defense, and 078 in Speed.
Greninja's BST is the same as Feraligatr's and its stats are 072 in HP, 095 in Attack, 067 in Defense, 103 in Special Attack, 071 in Special Defense, and 122 in Speed.
Ash-Greninja's BST is 640 and its stats are 072 in HP, 145 in Attack, 067 in Defense, 153 in Special Attack, 071 in Special Defense, and 132 in Speed.
Feraligatr can learn Normal-, Water-, Ice-, Fighting-, and Dark-type moves through level-up. It can learn Normal-, Water-, Ice-, Fighting-, Ground-, Flying-, Rock-, Ghost-, Dragon-, and Dark-type moves as TMs. It can also learn Normal-, Water-, Ice-, Rock-, Dark-, and Steel-type moves as egg moves.
Greninja (including Ash-Greninja) can learn Normal-, Water-, Psychic-, Ghost-, and Dark-type moves through level-up. It can also learn Normal-, Water-, Grass-, Ice-, Flying-, Bug-, Rock-, and Dark-type moves as TMs.
Feraligatr is a pure-Water-type: making it resistant to Fire, Water, Ice, and Steel; and weak to Electric and Grass.
Greninja is a Water/Dark-type: making it immune to Psychic; resistant to Fire, Water, Ice, Ghost, Dark, and Steel; and weak to Electric, Grass, Fighting, Bug, and Fairy.
By stats, Ash-Greninja has the highest BST of 640 compared to Greninja(530) and Feraligatr(530). Feraligatr has the highest HP stat(085), Defense stat(100), and Special Defense stat(083) compared to Greninja and Ash-Greninja(HP of 072, Defense of 067, and Special Defense of 071). Ash-Greninja has the highest Attack stat(145), Special Attack stat(153), and Speed stat(132) compared to Greninja(Attack of 095, Special Attack of 103, and Speed of 122) and Feraligatr(Attack of 105, Special Attack of 079, and Speed of 078).
By moves, both Greninja(Ash-Greninja) and Feraligatr can learn 5 different types of moves through level-up. Feraligatr can learn 10 different types of moves as TMs compared to Greninja(Ash-Greninja)'s eight. Feraligatr is the only one that can learn "Physical" egg-moves (6 of different type), but Greninja(Ash-Greninja) can learn Normal-, Water-, Poison, and Ground-type (4) "Status" moves as egg-moves.
By typing, Greninja has one more immunity than Feraligatr, has 2 more resistances than Feraligatr (which has 4), but has 3 more weaknesses than Feraligatr (which only has 2).