Actually i think that Choice Scarf + T-Wave can be good since you can cripple a sweeper with a scarf (allowing him only to do one hit) and then, you can paralyze him to render useless the Scarf.
With Choice Specs/Band you can do a favor to your opponent (even with Scarf, but its the least dangerous).
T-Wave/Toxic are better options over Yawn for the Sleep Clause, but, like you said, if you want cause your opponent to do lot of switches that's pretty good.
The choice item can be any really, technically speaking Band is the worst choice out there: sawk, swellow and zangoose whilst not enjoying the one-move limit will gleefully abuse it. Specs is a neutral ground: you can net some suprise KO's with the specs still on in a pinch, and if you at least have a lickilicky those specs will be useless. Except against something like gardevoir or exeggutor, but then both players are doing something wrong: the opponent for staying in/switching in against liepard, you for tricking it unto a special attacker. Scarf is useless if still on liepard: liepard doesn't need the extra speed in a pinch like say specs could give (note the could). And yes you can Thunder-wave afterwards, but this set is not necessarily meant to cripple sweepers, it's meant to screw over walls instead: Shuckle, Probopass, Seismitoad and lickilicky even with special attacks they will not appreciate the specs at all.
Not to forget that scarf can help
any sweeper who may or may not switch in, and if your team is slow good luck with that I'm afraid, whilst specs can only help special attackers: most of which are psychics to begin with.
Alas, it isn't difficult to know when to trick. If your opponent has a piloswine or another obvious stealth rocker (other than golem, for the love of god if you have a water or grass type, avoid tricking golem), feel free to use trick immediately to cripple them and force them to switch. With a mediocore defensive set it's possible to survive piloswine's attacks reasonably well, not to mention you get another trick chance with eviolite. Then pick off again with a yawn, forcing another switch, forcing your opponent needing to adapt immediately. Whilst giving you an easier time.
Status depends again, on the team: do you wish to slow sweepers down to help your own? T-wave. Do you want to wear down your opponent/do you lack toxic on any of your pokémon? Toxic. Do you want to force a lot of switches, and render another pokémon on your opponents side (along with a good trick) useless for a while? Yawn.
The EV Spread is kind of messed up, as a Specs Pokemon without max investment in SAtk (Hell you don't even have any) is not really good. Your EVs serve no purpose that I can see of. Mono-Dark coverage isn't extremely good in NU (Skunk does it well, but that's another story.) I'm not sure if I would use Liepard over any other Special attackers such as Haunter, SubCM Missy or even Murkrow, as all of them cover the same thing as Liepard. I think it should stick to it's standard sets, not that thinking out of the box is bad.
I think that ZandgaiaX use a choice item without investiments because the idea behind that set is that the first thing that you do with Liepard is to trick the opponent and possibly cripple him.
That's another hard duty because Liepard has few chances to switch to an attack without being hardly damaged due to poor defensive stats.
EDIT: And yeah, i don't see the point of that EV spread
Ok, yeah, I didn't read the whole set, just saw Specs + Dark Pulse. Well, it still doesn't matter because the EV Spread accomplishes nothing at all.
I am indeed not using Liepard as an attacker, using it as an attacker would be idiotic with such a great ability. It is however true that Liepard can be used as a semi-revenger with it's speed against ghosts like Golurk or Misdreavus or against pokémon with barely any health left, not to mention:
0 SpA Liepard Dark Pulse vs. 176 HP / 0 SpD Golurk: 186-222 (51.23 - 61.15%) -- 92.58% chance to 2HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 176 HP / 0 SpD Golurk: 282-332 (77.68 - 91.46%) -- guaranteed 2HKO
0 SpA Liepard Dark Pulse vs. 0 HP / 4 SpD Eviolite Misdreavus: 116-140 (44.44 - 53.63%) -- 33.2% chance to 2HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 0 HP / 4 SpD Eviolite Misdreavus: 176-210 (67.43 - 80.45%) -- guaranteed 2HKO
0 SpA Liepard Dark Pulse vs. 0 HP / 0 SpD Drifblim: 254-300 (57.59 - 68.02%) -- guaranteed 2HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 0 HP / 0 SpD Drifblim: 380-450 (86.16 - 102.04%) -- 12.5% chance to OHKO
0 SpA Liepard Dark Pulse vs. 4 HP / 0 SpD Gardevoir: 138-164 (49.64 - 58.99%) -- 99.61% chance to 2HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 4 HP / 0 SpD Gardevoir: 206-246 (74.1 - 88.48%) -- guaranteed 2HKO
0 SpA Liepard Dark Pulse vs. 132 HP / 0 SpD Exeggutor: 218-260 (59.89 - 71.42%) -- guaranteed 2HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 132 HP / 0 SpD Exeggutor: 330-390 (90.65 - 107.14%) -- 43.75% chance to OHKO
0 SpA Liepard Dark Pulse vs. 252 HP / 0 SpD Exeggutor: 218-260 (55.32 - 65.98%) -- guaranteed 2HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 252 HP / 0 SpD Exeggutor: 330-390 (83.75 - 98.98%) -- guaranteed 2HKO
0 SpA Liepard Dark Pulse vs. 240 HP / 0 SpD Musharna: 164-194 (37.87 - 44.8%) -- guaranteed 3HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 240 HP / 0 SpD Musharna: 242-288 (55.88 - 66.51%) -- guaranteed 2HKO
0 SpA Liepard Dark Pulse vs. 240 HP / 16 SpD Musharna: 158-188 (36.48 - 43.41%) -- 98.88% chance to 3HKO
0 SpA Choice Specs Liepard Dark Pulse vs. 240 HP / 16 SpD Musharna: 236-282 (54.5 - 65.12%) -- guaranteed 2HKO
That's major without any investment, with or without specs. The only useless calc is against drifblim with unburden, as you don't outspeed it. But then again, neither does scarf Raichu (<,<;). Yes, Calm Mind Misdreavus 'beats it', but you have encore, so you are clearly doing it wrong. Yes, Golurk and Drifblim have a huge chance of 1HKO'ing, but again: you're doing it wrong if you're switching in immediately.
The Psychics are even worse of, the best exeggutor can do is using sleep powder against it, but one has to wonder why they would keep in their exeggutor: an incredible pokémon in NU, against Liepard: especially if it gets locked into psychic by a choice item or encore. Giga drain is annoying, and Leaf Storm hurts, but with a good enough special wall/grass resist what are you complaining about? Gardevoir and Mushrana can indeed use calm mind against it, and then what? Get encore'd, yawned/toxic'ed/tricked and forced to switch out or wait: a perfect time for something like skuntank to clean it up from there. Liepard was and is never meant to be a sweeper, even the nasty plot set abuses prankster for a very good reason.
The EV spread on his Liepard set is the exact same setup as the very first set in Liepard's on-site analysis. You know, that hax set that made Liepard so famous. It's designed to optimize special bulk, give Liepard enough HP for a Leftovers number and to use Substitute 5 times instead of 4 (granted, his set isn't running Substitute), give enough speed to beat max speed base 95s, and the leftovers are placed into the Def stat.
He said himself that he didn't invent that EV spread. He just got it from this site's analysis.
This guy knows it ;), not to mention that that set is pretty much the 'bulkiest' that Liepard can ever reliably run. I can fiddle around with some of the EV's, but since most of Liepard's reliable switches are against walls/psychics, it's reasonable to give it full SpD ev's I think. But I'm not an EV/Calc. expert.
In the end however, Liepard functions best on a defensive team that can cover it's weaknesses (read: a lot of them), and that preferably uses both SR and Spikes. Of course a cleric and a wish-passer are enjoyable, but from personal experience running a defensive team without a wish-passer/cleric is hard.