Zoroark was Gen V's answer to Lucario that they did their best to hype up with a movie and locked it behind events. However Zoroark did not become as popular as its predecessor and thus became easier to access in later generations. Zoroark's main claim to fame is its Illusion ability, enabling mind games and causing your opponent to misplay and enabling Zoroark to take out key pieces of your opponents strategy. However Illusion is a paper thin with entry hazards and even moves used can quickly give up the game. Zoroark's frailty does not help matters, so it takes a deft hand to get the most out of Zoroark.
KitSpecs
Zoroark
Ability: Illusion
Item: Choice Specs
-Dark Pulse
-Flamethrower
-Sludge Bomb
-Focus Blast/Grass Knot/U-Turn
Nature: Modest (+SATK, -ATK) or Timid (+SPE, -ATK)
EVs: 252 SATK/252 SPE/4 HP
Zoroark makes a fantastic revenge killer, with above average base 105 speed and a blistering base 120 SATK. Specs allows Zoroark to smash whatever your opponent brings in and gives Zoroark the oomph to if not KO, at least compromise the opponent's pokémon to the point where its use is greatly hindered. Dark Pulse is STAB and hits brutally hard:
252 SpA Choice Specs Zoroark Dark Pulse vs. 252 HP / 0 SpD Jellicent: 356-420 (88.1 - 103.9%) -- 25% chance to OHKO
252 SpA Choice Specs Zoroark Dark Pulse vs. 252 HP / 252+ SpD Bronzong: 240-284 (71 - 84%) -- guaranteed 2HKO after Leftovers recovery
252 SpA Choice Specs Zoroark Dark Pulse vs. 252 HP / 40 SpD Xatu: 470-554 (140.7 - 165.8%) -- guaranteed OHKO
252 SpA Choice Specs Zoroark Dark Pulse vs. 252 HP / 4 SpD Espeon: 386-456 (115.5 - 136.5%) -- guaranteed OHKO
Flamethrower hits dangerous bugs like Vikavolt, Frosmoth and Escalvier (and Klefki) hard while enabling Zoroark to perform a good Salazzle impression. Ditto with Sludge Bomb wrecking Fairies that otherwise resist Zoroark's STAB (Comfey, Aromatisse, Gardevoir)
Final move is up to preference. Focus Blast is unreliable, but hits Umbreon hard.
252 SpA Choice Specs Zoroark Focus Blast vs. 252 HP / 252+ SpD Umbreon: 222-262 (56.3 - 66.4%) -- guaranteed 2HKO after Leftovers recovery
Grass Knot hits Seismitoad, Poliwrath, Rhyperior, Rhydon and others slightly to much harder than any of Zoroark's other moves. U-Turn is an excellent pivot move.
Dynamax
Dynamaxing works well with Zoroark's special sets as it has all the tools it needs. Max Darkness and Max Ooze both make Zoroark's Special attacks hit much harder and Max Flare sets up Sun, further boosting its own power and providing support to Sun oriented teammates.
Other Options
Heavy Duty Boots -Zoroark is often sussed out by entry hazards, so placing Heavy Duty Boots on can keep the illusion up a bit longer
Nasty Plot -not as immediate as Specs and will often tell your opponent that your pokemon is not what they are seeing, but Illusion can provide setup opportunities to have Zoroark muscle through most targets.
Trick/Taunt -Crippling a wall is always fun, though Zoroark still can't take a hit for beans.
Knock Off -Zoroark does have viable physical attack, but its viable Physical movepool consists of Knock Off, U-Turn, Low Kick, and Sucker Punch. Knock Off has good utility and is powerful, even on Special sets.
Preferred Partners
Entry Hazard removal is strongly recommended as mentioned before, Entry Hazards out Zoroark before it can begin and with how frail Zoroark is normally, the power drop from using the boots can be hard to justify. Otherwise, it is best to choose partners that help Zoroark abuse Illusion.
Illusion
Most obvious way to abuse Illusion is to have a Psychic weak teammate to bait Psychic attacks which Zoroark can absorb and often strike down the Psychic with a STAB Dark Pulse (or setup with Nasty Plot). However, Fighting types are not recommended as both they and Zoroark are weak to Fairy moves, so baiting out a Fairy attack will just ruin Zoroark before it can begin.
Another way is to have Zoroark disguise itself as an Entry Hazard setter to bait in Xatu or Espeon with Magic Bounce and then destroy them with a STAB Dark Pulse (be warned that Espeon is naturally faster than Zoroark and can carry Dazzling Gleam, so be careful).
Since Zoroark is often a special attacker, disguising it as a physical attacker can bait in a physical wall only to remove it from play with a powerful special attack. Also Zoroark enjoys having physically offensive teammates to break through the special walls that often trouble it.
Funny note, when I opened up the link for Zoroark, I had a minor glitch where the shiny and the normal variant were overlayed with each other.