Nasty Fox
Item: Life Orb
Ability: Illusion
Nature: Timid
EVs: 252 Speed, 252 SpAtk, 4 HP
- Dark Pulse (STAB attack, Flinch, More accuracy than Night Burst)
- Flamethrower (Assorted coverage, great Anti-Steel)
- Grass Knot (Takes out Rock types that resist Flamethrower and Bulky Waters)
- Nasty Plot (Boosts Special attack by two stages)
Dancing Fox
Item: Life Orb
Ability: Illusion
Nature: Adamant / Jolly
EVs: 252 Speed, 252 Atk, 4 HP
- Sucker Punch (STAB attack, Priority)
- Night Slash (Stable attack) / Aerial Ace (Anti-Heracross/Fighting Types)
- U-Turn (Scouting)
- Swords Dance (Boosts Attack by two stages)
I choose to mix it up!
Item: Choice Scarf
Ability: Illusion
Nature: Adamant / Modest / Jolly / Timid
EVs: 252 SpAtk, 252 Atk, 4 Speed
- Dark Pulse (STAB attack)
- Flamethrower (Anti-Steel/Bug (Anti-Forretress)) / Grass Knot (Anti-Rock/Water/Ground)
- U-Turn (Scouting)
- Aerial Ace / Focus Blast / Hidden Power / Extrasensory
Partners
Gengar is a great illusion to use. That's all I got, this guy is really better off flying solo. I do not recommend using moves that your illusion cannot use, or your opponent will figure out what's really behind the smoke and mirrors.
Countering
Even if he hides behind a Gengar illusion, Thunder Wave can still shut Zoroark down, unless he carries Sucker Punch. And even then, Zoroark will be severely hampered if luck is against him. After Zoroark is exposed, Fighting and Bug moves wreck him due to his awful defensive stats. Poor prediction with switch ins can lead to exposed Zoroarks, so he's better used as a revenge killer early on. Do not save him for the end when there's no pokemon left to act as illusions.
This is a signature that doesn't eat up an absurd amount of space.