Dusknoir

Pressure
Enemy attacks lose 1 extra PP. Increases wild encounter rate.
Type Tier
Ghost OU
Statistics
Min- Min Max Max+
HP
45
- 231 294 -
Atk
100
212 236 299 328
Def
135
275 306 369 405
SpA
65
149 166 229 251
SpD
135
275 306 369 405
Spe
45
113 126 189 207
Name Item Nature

Anti-Spin

Leftovers Careful
Moveset EVs
~ ThunderPunch
~ Fire Punch / Shadow Sneak
~ Will-O-Wisp
~ Pain Split
252 HP / 76 Def / 180 SpD

Thanks to his Ghost typing and good defenses, Dusknoir is a prime candidate for blocking attempts to remove spiking moves your team sets up.

There are four good Rapid Spin users in DP: Donphan, Starmie, Forretress and Tentacruel. Tentacruel and Forretress have no hope of breaking Dusknoir, so only Donphan and Starmie need special care. With the given EV spread, only Choice Band Donphan Earthquake can beat Dusknoir, and the far more common defensive minded Donphan will have to run from Dusknoir, or face having its attack power crippled with a burn from Will-O-Wisp. Starmie doesn't threaten Dusknoir much unless it is carrying Choice Specs, so you can hit it with ThunderPunch or Shadow Sneak and leech its HP with Pain Split. The only Rapid Spin user Dusknoir fears is Torkoal, who takes laughable damage from his attacks. The fiery little tortoise threatens to seriously hamper Dusknoir's offensive and defensive capabilities with a Will-O-Wisp of its own. Thankfully, the presence of Torkoal in the OU tier where Dusknoir resides is very rare.

Fire Punch prevents Heracross from abusing Guts by coming into a Will-O-Wisp and Pursuiting Dusknoir. Other common Pursuit users such as Tyranitar and Metagross can be hit with a burn. Will-O-Wisp and Fire Punch make Weavile much less of a threat too. Shadow Sneak is a reasonable option here as it bypasses his awful Speed and can help to finish off weaker Pokémon, most notably Azelf.

Pain Split is a rather poor method of healing, but it's all Dusknoir has outside of the very risky Rest. However, you can use his ridiculously low HP and Speed to your advantage by taking hits from high HP Pokémon and sapping their health while recovering your own.

Name Item Nature

Resttalk

Leftovers Careful
Moveset EVs
~ ThunderPunch / Brick Break
~ Fire Punch / Shadow Punch
~ Rest
~ Sleep Talk
252 HP / 76 Def / 180 SpD

As was mentioned in the comments on the previous set, Pain Split isn't a great way to heal so you can use Rest and Sleep Talk in tandem to keep Dusknoir around longer.

Will-O-Wisp is absent from this set as it will conflict with any Toxic Spikes you may have already set up, so you'll need to take a more offensive approach to Pursuit users. Brick Break will hit Tyranitar and Weavile, while Fire Punch will assist in taking down Heracross and Metagross. Shadow Punch or ThunderPunch will make sure Starmie runs and the latter means he can still function as your coverage against Gyarados. Ice Punch is also an option here as without it, you're inviting Dragons to switch in for free.

Name Item Nature

Calm Mind

Leftovers Modest
Moveset EVs
~ Calm Mind
~ Ice Beam / Focus Blast
~ Shadow Ball / Will-O-Wisp
~ Pain Split
252 HP / 252 SpA / 4 Spe

Calm Minding isn't really the best use of Dusknoir's talents, but it's there and it works. Shadow Ball / Focus Blast hits everything neutrally, but Ice Beam is more reliable as a secondary move.

With Will-O-Wisp over Shadow Ball, you can take hits from both sides, but with only a non-STAB Ice Beam in the way of offense, you'll take a while to stall out some of the more defensive Pokémon around.

Name Item Nature

Choice Band

Choice Band Adamant
Moveset EVs
~ Shadow Punch / Shadow Sneak
~ Fire Punch
~ Focus Punch / Earthquake
~ Ice Punch / ThunderPunch / Pursuit
252 HP / 252 Atk / 6 Spe

An attempt to take advantage of Dusknoir's decent attack and movepool. The biggest problem with this set is a lack of good physical STAB—Shadow Punch really just doesn't do it. Shadow Sneak can work nicely over it and can OHKO a Gengar or Alakazam before they get a chance to throw a Shadow Ball at you. Fire Punch and Focus Punch / Earthquake are recommended for Heracross and Tyranitar / Heatran respectively.

Ice Punch can down a Dragon and does decent damage to Gliscor, while ThunderPunch hammers Gyarados. Pursuit will hurt a fleeing Starmie, but will not OHKO.

Other Options

Dusknoir is a really good Pokémon to set up Trick Room—it has high defenses and it doesn't mind the negative priority. Counter is a good option for surprising powerful physical attackers like Heracross who want to 2HKO you—just don't overuse it, as Dusknoir isn't ideal for the move with his pitiful HP.

EVs

You'll want to max out that abysmal HP first. While leaving it untouched would make Pain Split more powerful, Dusknoir's base HP is so bad that it'll make little difference. You can split the remaining EVs between the defenses or focus on one. Special Defense helps against Starmie, Azelf and the like while Defense EVs will cushion the blow from physical attackers like Donphan and Heracross. Attack EVs aren't overly helpful, although it is worth noting that around 294 Attack (232 EVs) will give Dusknoir a 100% chance to 2HKO Azelf with Shadow Sneak, assuming Azelf has 4 HP / 0 Defense and no Leftovers. If Azelf has a Life Orb, Dusknoir is guaranteed to 2HKO it with Shadow Sneak with 241 Attack (20 EVs).

Adamant with max Attack and HP if you're using the Choice Band set.

Opinion

Possibly the most unnecessary evolution in DP, Dusknoir is about as good as Dusclops was in ADV. The extra Attack helps in a few places—such as countering Gyarados with ThunderPunch—but Dusknoir sorely misses good STAB. Generally, Dusknoir is relegated to Dusclops' old duties, namely blocking Rapid Spin and countering a few specific sweepers.

Counters

As mentioned, Heracross can be a real pain for Dusknoir. However, it is the presence of Heracross that really hurts—Dusknoir has to be very careful about Will-O-Wisp if Fire Punch is absent from its moveset, lest it find itself facing certain destruction. Unfortunately, Will-O-Wisp is Dusknoir's main answer to its other greatest fears: Tyranitar, Metagross and Weavile. As a result, it is best to find out which of Dusknoir's counters are present before bringing it out, then act accordingly. Houndoom and Absol are also potentially devastating against Dusknoir with their potent STAB Dark attacks. Umbreon also gets Pursuit, and will use Synchronize to toss Will-O-Wisp right back at you, but Pursuit doesn't do that much damage. Heatran is a counter unless Dusknoir has Earthquake or can predict with Focus Punch. Flash Fire boosted Fire attacks from Heatran's massive Special Attack can easily fell Dusknoir in one hit. Toxic and Will-O-Wisp in general hurt Dusknoir, who usually relies on Pain Split for healing.