In Generation IV, Game Freak introduced an event legendary with nice stats, a decent offensive typing and such an elegant movepool, including its signature move Dark Void. It was quickly moved to the Ubers tier, swiftly becoming a top tier threat. However, it had one drawback that prevented it from being such a potent threat; the Sleep Clause. Even with this clause, Darkrai continued to be an incredibly useful attacking force for three generations, retaining its status as the dangerous Pokemon it's known to be. When Anything Goes was created, there was no Sleep Clause existent so Darkrai was free to abuse Dark Void to its fullest potential. Without a Sleep Clause it would only make sense that Darkrai would be a much more potent threat, however not only has its effect on the metagame changed; it has also achieved a different usage method.
Substitute
With the ability to induce sleep on multiple Pokémon comes the necessity to gain some form of protection to allow it to Dark Void multiple Pokémon seamlessly. By giving it this extra layer of defense, Darkrai can disable the opposing team without receiving major damage due to its relatively low defensive stats. Priority being omnipresent within the Anything Goes metagame means that Darkrai benefits immensely from having a way to shield incoming Extreme Killer Arceus and Mega Rayquaza. Substitute provides it with this defensive backbone, it would otherwise not have.
This of course leaves two moves, that can vary between sets.
Attacks:
Dark Pulse - Dark Pulse is the main choice for an offensive move on Darkrai due to its decent offensive typing and boost to power through STAB. It also has a 20% flinch chance which can be somewhat useful against Pokémon with an alternate status infliction or immunity to the sleep condition. This move pairs well with almost anything else listed here, however pairing it with Foul Play can be somewhat redundant due to the double Dark-type STAB.
Sludge Bomb - Sludge Bomb is the best choice for extra coverage on Darkrai as it can struggle breaking defensive threats of Fairy-typing without relying on set-up. However, it can be somewhat detrimental with its 30% Poison chance, if a Pokémon is not currently asleep, however poison damage can be stalled out with spamming Substitute if necessary. This pairs well with Dark Pulse mainly, as Dark+Poison is Darkrai's best offensive coverage option.
Thunder - Thunder is another alternative coverage option for Darkrai, however only really hits Ho-Oh and Kyogre which are already dealed with efficiently without the extra dedicated coverage. In fact, Sleep Talk variants of the two aforementioned threats would ideally be prevented through the use of Taunt. Thunder is best paired with Dark Pulse, but is probably not the ideal choice for a Substitute Darkrai set.
Focus Blast - Focus Blast is an option to hit Tyranitar, Ferrothorn, Klefki and other defensive threats; however, this is quite difficult to fit on any set due to the rarity of the former two Pokémon and the lack of damage towards the latter. It also provides extra damage if one was to require the crippling of an Extreme Killer Arceus or opposing Darkrai; however Dark Pulse can efficiently deal with these regardless. Focus Blast is best paired with Dark Pulse.
Foul Play - Foul Play is an alternative STAB option that is usually outclassed by Dark Pulse however is incredibly effective when paired with Swagger. Otherwise this move is quite underwhelming. Foul Play should only really be paired with Swagger, however in very specific scenarios it can function against physically offensive set up sweepers and paired with Will-O-Wisp.
Ice Beam - Ice Beam is an option to hit Mega Rayquaza, Mega Salamence and Shaymin-Sky for maximum damage. It can also function against rare checks such as Toxic Orb Gliscor, although is usually not worth the slot. It can be paired with Dark Pulse.
Hidden Power Steel - Hidden Power Steel is an extremely niche option to bait and eliminate Mega Diancie, and is otherwise useless. It should only be paired with Dark Pulse.
Status:
Nasty Plot - Nasty Plot is Darkrai's ideal secondary choice after Dark Pulse as it allows set up during an opposing Pokémon's sleep turns. At +6, Darkrai doesn't have much trouble with the majority of the metagame, however can struggle with some defensive threats and sometimes prefers alternative options due to this. The main reason for this not being the only option is the difficulty in getting to +6 against different dedicated checks namely Scarf Xerneas, Sleep Talk Ho-Oh and Mega Diancie. Nasty Plot should only be paired with Dark Pulse; however, some niche sets may run an alternate attack such as Focus Blast to hit Arceus better.
Taunt - Taunt is a prevention to a large amount of Darkrai's checks including Sleep Talk users (Ho-Oh, Primal Kyogre, e.t.c.) and Pokémon that use recovery on wake up, while it can also provide a stop to Defog if the opposing team is quite weak to Stealth Rock or alternate hazards. A major reason for this being used instead of Nasty Plot is the difficulty of set-up and the requirement to stop the aforementioned checks. Taunt is best paired with Dark Pulse.
Double Team - Double Team is the "I'm an awful person option" and is quite effective at making your opponent forfeit. Just get to +6 Evasion without much difficulty and then watch your opponent cry, call you a prick and then leave. In all seriousness, Double Team is incredibly luck reliant and when paired with such a luck dependant Pokémon in Darkrai, it can be borderline impossible to set up when accounting for all opposing teams. Without the presence of Nasty Plot, Taunt or an alternate coverage option; Darkrai can be PP stalled easily by many bulky Pokémon. Double Team should only be paired with Dark Pulse.
Swagger - So imagine this scenario. You've had a long hard day of working, and then after your dedication you get fired. Angry as hell, you storm into your house, load up your PC and hop onto a Pokémon simulator thinking of ways to take out your anger on others. You see this metagame Anything Goes and you click it. If you're serious about unleashing your anger there's one thing you can rely on. Swagger is an incredibly easy way to piss off your opponent, so why not use it? On top of the sleep condition, they might have trouble attacking when they wake up. This sounds incredibly broken, but it isn't. As you can see, there is only a certain amount RNG can help you in a game. You might not want to rely your whole set on RNG. However, when it gets the coin flips it requires, it is incredibly hard to take down without Mega Diancie. Swagger should be paired with Foul Play.
Disable - Scarf Pokémon being one of Darkrai's largest threats, can be checked efficiently with the use of Disable if you're already behind a Substitute. Allowing you to set up your Substitute again and damage the opposing team. Disable may also disallow certain moves from effecting Darkrai, but in most regards (other than stopping Scarf Pokémon) is outclassed by Taunt. Disable should be paired with Dark Pulse.
Thunder Wave - Another option for stopping Scarf Xerneas, Thunder Wave allows a permanent solution instead of the temporary Disable. However, even with Paralysis status applied, Xerneas can still break through and hit Darkrai. Darkrai therefore usually requires a switch after the status has been applied, or can rely on Dark Pulse flinches and full paralysis if it can set up a Substitute. Using Thunder Wave on the wrong Pokémon can be incredibly detrimental as you can no longer induce sleep on it. Hence Thunder Wave is very iffy when it comes to viable Substitute Darkrai sets. Thunder Wave can be paired with Dark Void, or ran over Dark Void; however if done, this eliminates Darkrai's main niche.
Will-O-Wisp - Will-O-Wisp is an option to disable physically offensive attackers such as Extreme Killer Arceus and non-Lum variants of Mega Rayquaza, while disabling Darkrai checks such as Scarf Zekrom. However, like Thunder Wave, if this condition is applied to the wrong Pokémon, Darkrai can almost become useless. Be extra careful when using this move. Will-O-Wisp should only be paired with Dark Pulse, or in rare situations Foul Play (see Foul Play section for more details)
Other Less Viable Options:
Knock Off - Knock Off can be used to remove Choice Scarfs from opposing Xerneas and Zekrom, remove Lum Berries from Arceus and Rayquaza and remove offensive items to act as some form of team support, however. While removing these items is extremely beneficial in some cases; it is often preferred that you use Disable (to disable Scarf abusers) or your status option (to remove Lum) instead of dedicating a slot.
Sucker Punch - Sucker Punch isn't an extremely viable option due to the innefficiency of running Physically oriented Darkrai. Darkrai's biggest threats include Extreme Speed users and Fairy-types regardless, so usually Sucker Punch either hits for minimum damage or no damage at all.
Toxic - Toxic is an alternate option for wittling down an opponent's Hit Points, however doesn't benefit against most of Darkrai's checks, and is usually more detrimental than other options.
Swords Dance - Swords Dance is an option if you do end up opting for a physically oriented Darkrai set, however Nasty Plot is a better option due to Darkrai's special movepool being much better than its physical movepool. Also Darkrai's SpA stat is higher than its Atk stat by a relatively high amount.
Power-Up Punch - If you're this desperate to run Physically oriented Darkrai, please just run Swords Dance. If you're trying to be this unique, you've gone too far. Hi
Thimo.
Overall Substitute Darkrai is an incredibly diverse Pokémon with a plethora of alternate options. Rather than just read about all the combinations, why not try some yourself. Who knows, maybe you'll find a nice option not listed above, or potentially a different combination. Have fun preparing for Darkrai!