well there are several ways to use Feraligatr:
Feraligatr @ Choice Band
Impish Nature (+Def, -Sp Atk)
216 HP/188 DEF/104 ATK
-Waterfall
-Ice Punch
-Brick Break/Superpower/Crunch
-Earthquake
defensive CB Feraligatr. what i use as a starter. very effective.
Feraligatr @ Leftovers
Adamant Nature
252 HP/108 SPD/148 ATK
-Waterfall
-Ice Punch
-Earthquake
-Dragon Dance
quite basic.
Feraligatr @ Salac Berry
Jolly Nature
252 SPEED/252 ATK/4 HP
-Waterfall
-Ice Punch/Rock Slide
-Swords Dance
-Endure
basic workings of swarm heracross, passed onto gatr. rock slide is so that gyara and water absorbers don't wall you. endure being a TM opened up many possibilities.
Feraligatr @ Life Orb/Expert Belt
Adamant Nature
252 ATK/196 HP/60 SPD
-Waterfall
-Ice Punch
-Earthquake
-Agility
bring in, agiligize, and start shooting attacks like crazy.
finally,
Feraligatr @ Leftovers
Naughty Nature (+Atk, -Sp Def)
252 ATK/124 SP ATK/132 SPD
-Waterfall/Crunch
-Surf/Hydro Pump/Ice Beam
-Focus Punch
-Substitute
subpuncher. surf/ice beam is for physical walls who can't take much of a special hit. crunch is an option if you're not fond of starmie, gengar, alakazam and the like.