Moveset Name: SubLiechi Sweeper
Move 1: Substitute
Move 2: Flail
Move 3: Aqua Jet
Move 4: Swords Dance / Earthquake / SuperPower / Ice Punch
Item: Liechi Berry
EVs: 4 HP / 252 Atk / 252 Spd
With a mediocre 78 Base Speed, Feraligatr needed to rely on Dragon Dance to gain potential as a fast threat. That call was answered with HG/SS, which gifted Feraligatr with Aqua Jet. Running similarily to the SubSalac Set which used to use Salac Berry to increase his Speed, Feraligatr now has Aqua Jet as a STAB priority. This set utilizes two main concepts: First, substitute your way down to activate both Liechi Berry AND Torrent. Then let loose with Aqua Jet.
Flail, further powered by Feraligatr's low HP, coincides with Aqua Jet for perfect neutral coverage. The last move is up to preference. Earthquake is arguably one of the best attacking moves in the game, and is a viable choice on this set, hitting Electric-types for SE damage on the switch-in, while SuperPower handles Registeel and Ice Punch picks off Grass-types such as Torterra, Tangrowth, Leafeon, and even Altaria, who takes 4x from the attack. Swords Dance, something that sets Feraligatr apart from Gyarados, can also be used to further Aqua Jet's power.
The EVs are run so that regardless of Liechi Berry, Feraligatr contains monstrous Attack and good Speed throughout.
Any form of bulky water usually causes stress for this set. Milotic can come in on impunity, take a Flail, and hit back with either Hypnosis or Hidden Power Grass. Spiritomb also causes problems, due to being able to burn you with Will-o-wisp, halving your Attack power as well as being respectably bulky as well. Registeel has massive defenses and can come in on anything bar SuperPower or Earthquake. Bulkier variants of Altaria can also handle Flail, but fear an Ice Punch.
[I don't know why I posted threats, they're just...there.]