Alright, time to get the ball rolling!
New Overview
Zoroark is all about fighting dirty, using sneaky tricks and underhanded tactics to win matches. It achieves this by utilizing its signature ability, Illusion, which allows to appear as the 6th slot Pokemon on your team. This can lead to some pretty tricky mindgames, as your opponent has no idea if you've sent Zoroark out or not. That Scizor that just switched in might be secretly a Zoroark in disguise that's just waiting to roast your Skarmory with Flamethrower. Your Heatran might not stop that Jirachi if it happens to carry Focus Blast. When all's said and done however, Zoroark is burdened with several limitations that prevent it from being an absolute murderer. It's disappointingly frail, to the point where it can never switch into anything and any remotely powerful attack will OHKO it. It relies on its Speed to KO opposing Pokemon, but 105 Base Speed is a step below several prominent Pokemon, notably the Swords of Justice, Gengar and Tornadus-T. Still, when it comes down to it, Zoroark is the perfect assassin, taking out unaware targets with impunity. Just don't let it get caught outside of the shadows.
Old Overview
Zoroark is blessed with awesome attacking stats, a great Speed stat, and a plethora of move options, making it an offensive threat to watch out for. Access to both Nasty Plot and Swords Dance makes it an unpredictable and effective sweeper, which allows it to pose as a major threat to both offensive and stall teams. However, the main draw to using Zoroark is its unique ability Illusion, which allows it to take on the appearance of the last Pokemon on your team. When properly used, Illusion can temporarily trick the opponent into thinking Zoroark is a different Pokemon altogether, which can allow it to get a surprise kill or even set up. Illusion works well with Zoroark's incredible coverage, which, when paired with Sucker Punch, allows it to take out the vast majority of the metagame. However, Zoroark's miserable defenses mean that almost any strong STAB or super effective priority move will OHKO it. Zoroark's typing also pales in comparison to that of Gengar or Lucario, and it has a hard time switching in. As a result of this, Zoroark is a difficult Pokemon to use and unforgiving if you make a mistake. However, despite these flaws, Zoroark is still a solid Pokemon; a successfully executed feint from Zoroark can instantly turn the tide of the match.
Why it was changed: The old analysis had too much hype.
Way too much hype for a Pokemon that wasn't even OU. Illusion is useful, but even if you use it properly, it'll hardly
turn the tide of battle. The overview mentions Zoroark's frailty, but there was too little emphasis on Zoroark's second biggest flaw; its "good-but-not good-enough" Speed stat. I've corrected these issues, and toned down the hype (while also giving its fair due).
Note: I am aware of the fact I use some text from its "counters" section, i'll be revamping its counters section too.