So if you want to have lots of fun with a Hisuian Zoroark on your team, you need to do two things:
Step 1: Have a way to reliably spread lots of status before Zark hits the field, because Zark loves to run item Hex. This is kind of hard at the moment because Iron Moth is absolutely everywhere and eats Toxic Spikes, but a defensive thunder waver could also work. If you're struggling, the bare minimum should be Zark and the Skeledirge you will be partnering with both running Will-O-Wisp. This is often way too hard to set while maintaining the disguise, but will at least let you play ball with free turns that either one gets.
Step 2: Abandon the idea of the "optimal" Skeledirge set. You can have Torch Song, and if you've really got Step 1 down pat and good game sense, Earth Power, but you're probably not getting Slack Off. Here's the deal. Zark and Dirge share Will-O, but if you didn't have to fall back on this, there's your in for Earth Power on Dirge. As special-oriented Ghost types that aren't trash, Skeledirge and Zoroark both have Shadow Ball. But to really sell the disguise while allowing Zoroark to have the anti-Kingambit option of Flamethrower, your Skeledirge will have to run Flamethrower as well. Even if Dirge never uses it, you don't want the opponent to have a move they can point to and say "this Dirge is real" or "this one's an illusion" until the moment you want to let Zoroark take damage or reveal the true Skeledirge. Dirge can run Torch Song for when the jig is up, while Zark can use Comeuppance as a tech for certain faster threats like Meowscarada or a speed-boosted Iron Moth, getting the aid of a Fire Tera if one is worried about a Knock Off KO or boosted Fiery Dance souring things.
The main reason to use this combo is how similar Dirge and Zark can appear, while their answers are markedly different. Ghost!TB Meteor Dragapult will erase Skeledirge, but Zark will take zero damage and blast it back with Shadow Ball, or set wisp and force Pult to switch next turn. If the opponent's fires are dead, you get your free wisp guaranteed even if Zark had to switch in to the Ghost Meteor as it was used. Meanwhile, Darks will eat Zark for breakfast, but hesitate to do so at a Dirge disguise because if the real Dirge is out instead, Tera Fairy will shrug the Dark move off and let Dirge get going really easily.
But the best thing about having such a specifically seamless disguise is that, if you play your cards right, if Dirge is down, Zoroark is still full and the Illusion disguise changes to another full-HP mon, your opponent might actually forget that Illusion is still in play. If you're going to play this mind game, pick the slower Pokémon in your team to fill the fourth, fifth, and sixth slots when choosing your order, in order to let Zoroark's 350 speed tier get the jump on someone who thinks they can outspeed something like a Stinger Qwilfish. It's not the easiest thing to pull off if your opponent pays attention and has good game sense, but few things are as satisfying as tricking your opponent twice.