Edit: I recently got some flak for this journal, so I will say this now. THIS IS BY NO MEANS A COMPREHENSIVE ANALYSIS. THESE ARE MY OWN OBSERVATIONS DURING ONLINE BATTLES - YOU USE THIS INFORMATION AT YOUR OWN DISCRETION. FOR PROPER ANALYSIS AND RECOMMENDATIONS, GO TO SMOGON OR GAMEFAQS.
Because I haven't posted anything in awhile. Plus, this has been mulling over in my head for some time.
Dusk Form Lycanroc takes a little from both its Midday and Midnight forms, offering above average Speed and Attack while giving it a hard-hitting move pool with coverage moves like Fire Fang, Thunder Fang and Iron Head. This coupled with Tough Claws and Swords Dance makes Dusk Form a threatening mid to late game sweeper against balanced and offensive teams alike, letting it act as a soft check for tanks like Tangrowth and Snorlax while also letting it outspeed glass cannons like uninvested Gengar, Zoroark and Mega Charizard X. On the downside, Dusk Form suffers from terrible defensive bulk, making it easier for revenge killers like Ash-Greninja or Mega Absol to pick it off, especially with Life Orb recoil. Dusk Form is also vulnerable to all entry hazards as well as status, making it difficult to set up without proper team support like Florges, a support Eeveelution or a good baton passer. While its Attack stat is good, it's still not high enough for Dusk Form to power through physically defensive walls like Mega Aggron or Shuckle without additional Swords Dance boosts, giving the opponent chances to setup. Nonetheless, Dusk Form remains a decent choice for Rock type lovers who want a faster alternative to the Rock type's otherwise less than stellar speed without sacrificing too much coverage or relying on Trick Room.
Swords Dance Attacker
Stone Edge/Iron Head
Thunder Fang/Fire Fang
Item: Life Orb/Lycanium Z
Ability: Tough Claws
EVs: 252 Atk / 4 HP / 252 Spe
Swords Dance bolsters Dusk Form's Attack to excellent levels, making it a threatening late game sweeper. Stone Edge gives Dusk Form a powerful STAB move that threatens Flying and Ice types, and can be powered into Splintered Storm Shards if running Lycanium Z. If you already have a Z move on your team, Iron Head is a more accurate alternative that offers coverage against opposing Rock types like Shuckle, Gigalith and opposing Lycanroc without sacrificing too much power. Iron Head also gives Dusk Form a powerful answer to bulky Fairy types like Sylveon, Florges and Mega Altaria, who cannot comfortably switch into an Iron Head at +2. Accelerock gives Dusk Form a useful STAB priority move that's boosted by Life Orb, Swords Dance and Tough Claws, letting Dusk Form pick off weaker or frail opponents without worrying too much about Speed. Fire Fang is a useful option for Steel types like Skarmory and Mega Scizor while also punishing slower Grass types like Lilligant lacking Choice Scarf, Lurantis and Tangrowth. Thunder Fang on the other hand deals heavy damage to Water types like Empoleon, Samurott and Keldeo, who would otherwise wall Dusk Form with their bulk or OHKO it with their STAB moves. If greater overall power is needed, Crunch can be used to hit Psychic and Ghost types hard. Crunch also has a chance to lower the opponent's Defense, softening up walls that could otherwise keep Dusk Form from sweeping.
Maximum investment in Attack and Speed lets Dusk Form hit as hard and as fast as possible. A Jolly nature lets it outspeed glass cannons like Adamant Mega Salamence before Dragon Dance, Timid Keldeo, Mega Gallade and Ash-Greninja. Adamant nature gives Dusk Form the extra oomph to OHKO Skarmory, Tentacruel and Oricorio at +2 after Stealth Rock damage, and 2HKO Dusknoir and Tangrowth. The remaining EVs can go into any other stat save Special Attack, though HP is most recommended to help mitigate Curse damage and recoil from Life Orb. Life Orb helps bolster non Rock type moves, letting them hit harder. If you don't run any other Z moves, Lycanium Z gives Dusk Form a one time nuke with perfect accuracy, though it lacks the extra power boost from Tough Claws.
While Dusk Form could be set out at the beginning of battle, it generally dislikes having to do so as it needs to use Swords Dance at least once before it can perform a sweep, potentially giving the opponent a free KO or time for their own setup. As with any stat boost set, try to time Swords Dance when the opponent is attempting a switch or uses Wish/Protect to give Dusk Form the chance it needs. If you use it later in battle, ensure you have at least one Pokemon that can clear hazards like Defog Smeargle, Altaria or Mega Blastoise. Dusk Form also heavily dislikes status, as it cannot viably run Facade even with Life Orb and Tough Claws, so don't switch it in unless you have a reliable cleric. Take care to watch out for Trick Room users as well - while it's not the fastest Rock type out there, its base 110 Speed can make it vulnerable to Trick Room setters like Slowking and Carbink, who can withstand an Accelerock at +2 even with Life Orb and potentially score a KO with their STAB moves.
Dusk Form works best with mixed or bulky Pokemon like Celesteela, Clefable and Mega Medicham who can clear out its checks with their attacks or stall them. Fire types like Mega Blaziken, Magmortar and Heatran can help counter Grass types who try to apply pressure. Pokemon who can take Mach Punches like Rocky Helmet Weezing are also appreciated, as Mach Punch from the likes of Breloom and Conkeldurr can OHKO Dusk Form even before Stealth Rock damage. Dragon types like Goodra and Drampa are also great teammates, since they can take Grass and Water type moves for Dusk Form and counter with their own coverage moves. As with Midday Form, Choice Scarf Lilligant can also be an excellent partner to help pressure opposing Ground types and possibly put Dusk Form back in top condition with Healing Wish. Though you risk losing momentum, Dusk Form will also welcome clerics like Mega Audino, Vaporeon, and Florges thanks to their massive HP recovery in Wish and possibly healing status with Heal Bell.
Drill Run, Iron Tail and Zen Headbutt are all stronger alternatives to Iron Head, but are generally less reliable thanks to their imperfect accuracy. Brick Break is an option that can help Dusk Form fight back against Steel types while also destroying the opponents screens, but is less useful as coverage and cannot viably fit onto a set running Lycanium Z. Dusk Form can run Hone Claws for an extra accuracy boost, but the loss in extra Attack boost is quite noticeable. Bulk Up is also an option to boost Dusk Form's Defense while still upping Attack, but the extra defense is very situational and relies more on luck than anything else. A harder hitting set with Giga Impact, Outrage, Swords Dance and Sucker Punch with Dragonium Z can be used, but is even more situational and generally inferior due to a lack of coverage and risk of self KO'ing due to confusion. Dusk Form also has the speed to set up Stealth Rock, but is not as reliable as other setters due to its terrible bulk and dislike of going first. Finally, while Dusk Form can run Last Resort as a powerful substitute for one of its moves thanks to it benefiting from its additional buffs, it requires using every other move first, which is very risky if Dusk Form hasn't already started a sweep.
Checks and Counters
Bulky Ground types: Bulky Ground types like Claydol, Torterra and Gastrodon can stall Dusk Form and heal off any damage given to them, even Splintered Storm Shards at +2. Torterra must watch out for Fire Fang if Dusk Form is running Life Orb, however.
Fighting types: Fighting types can resist Dusk Form's STAB attacks and counter with their own STAB moves, either by access to priority in Mach Punch or with greater speed such as Choice Scarf Primape. Slower Fighting types like Poliwrath and Hitmonchan lacking Choice Scarf must watch out for the rare Zen Headbutt however, as they cannot switch into one at +2, especially with Life Orb.
Steel types: Choice Scarf Togedemaru is a dangerous counter to Dusk Form, who can take a boosted Accelerock and doesn't even fear Fire Fang thanks to Iron Barbs and Spiky Shield. Celesteela is also a notable check to Dusk Form, as it can take advantage of a burned or paralyzed Dusk Form to set up Leech Seed or possibly OHKO it with Giga Drain or Flash Cannon. Ferrothorn is also a fantastic counter to sets not running Fire Fang, as it can switch in to Splintered Storm Shards and survive long enough to OHKO Dusk Form with Power Whip or Gyro Ball.
Physically Bulky Walls: Even with the extra boost in power from Tough Claws and possibly Life Orb, physical walls like Golem, Weezing and Regirock can still annoy Dusk Form by absorbing an unboosted attack and retaliating with their own coverage moves. They especially like sets with Lycanium Z, as attacks from that set are notably weaker without Life Orb and can even take a Splintered Storm Shards with little trouble. Even if they can't KO it, they can still stall Dusk Form and rack up Life Orb recoil for an easier kill.
Listening to: Battle! Team Rainbow Rocket
Watching: Game Grumps
Playing: DARK SOULS 3 The Fire Fades Edition
Drinking: Ramune Blue Raspberry