This right here is a pretty good Feraligatr set that I use myself, and it has worked wonders for me:
Feraligatr@Life Orb/Expert Belt/Muscle Band/Wacan Berry
Adamant/Jolly
252 ATK, 252 SPE, 4 HP/SPD/DEF
-Waterfall/Aqua Tail
-Ice Punch
-Earthquake
-Agility
After one Agility, this thing is a nightmare, but if you can pull of two/three...your opponent needs to play carefully. Waterfall or Aqua Tail for STAB(Same Type Attack Bonus, boosts the move by 50% if it is the same type as your pokemon, which this is) depending on how you feel about Aqua Tail's accuracy. Earthquake takes care of pesky Electrics, while Ice Punch can rid you of the Electrics that aren't hit by it, as well as destroy Gliscor and Dragons.
This thing is pure terror because you have a good chance of pulling off at least one Agility, which will double the 'gatr's speed, and possibly put you int Torrent range as well, adding on to the damage output. The choice of item is dependent on your tastes: Life Orb gives the best power boost, but also has the recoil drawback, but that can give you Torrent, so it's kinda hard to decide there. Expert Belt for Super-Effective hits, which you'll more likely than not be dealing out, but if you can't, Muscle Band helps as well. Wacan Berry is just for if you feel that he won't be surviving an Electric attack.
Even against other Water-Types, STAB-boosted, Item-boosted, and possibly even Torrent-Boosted Waterfall/Aqua Tail will hurt. Feraligatr has pretty good natural bulk, but you can forego the listed EVs for more defensive ones if you so wish.