Drifblim's most common set acts as a very threatening late-game sweeper. However, keep in mind that Unburden's effect disappears as Drifblim switches out, so choose an effective moment for it to set up and to eat its Berry carefully. Calm Mind allows Drifblim to attempt a sweep thanks to the Special Attack boost. The added boost in Special Defense is very handy in a metagame where fast special attackers are common, as it makes Drifblim harder to revenge kill before Unburden is activated. Substitute is meant to be used repeatedly until Drifblim eats its Berry; it also allows Drifblim to play around Sucker Punch users, to escape Pursuit, to protect itself from revenge killers before Unburden activates, and to avoid status. Shadow Ball is Drifblim's best STAB attack that hits Psychic-types such as Slowking, Gardevoir, and Jynx hard, all of which are very common threats. Hidden Power Fighting gives Drifblim perfect coverage alongside Shadow Ball that allows it to hit Regirock, Cradily, Magneton, Lickilicky, Regice, and Dark-types not named Skuntank super effectively.
The given EV spread allows Drifblim to outspeed Choice Scarf Timid Manectric after the Unburden boost, which is likely the fastest revenge killer it will face aside from the somewhat rare Choice Scarf Tauros. The Special Attack is maximized so Drifblim is guaranteed to OHKO Tauros, Floatzel, and Manectric and to 2HKO Regirock after a Calm Mind and Stealth Rock damage. However, the EV spread is pretty customizable, depending on what you need. For instance, 140 SpA / 124 SpD / 244 Spe ensures that Drifblim's Substitute won't break to Slowking's Surf after a Calm Mind, but you'll miss some of the crucial aforementioned KOs.
The chosen Berry depends mostly on personal preferences; Sitrus Berry doesn't require Drifblim to be at very low health, which means it may activate Unburden sooner, and grants it an additional Substitute. Petaya Berry, on the other hand, is very helpful if Drifblim faces too much pressure to set up manually with Calm Mind.
Hidden Power Ground is an appealing option, since it 2HKOes Skuntank even when unboosted, but it leaves Drifblim completely walled by Dodrio and much more vulnerable to other Dark-types, namely Shiftry and Cacturne. Hidden Power Flying provides a secondary STAB option that hits all of Skuntank, Vileplume, Hitmonchan, specially defensive Cacturne, Poliwrath, and Meganium, at the cost of leaving Drifblim weaker against Regirock, Cradily, Magneton, and Tauros. Status moves like Will-O-Wisp can prove to be useful to cripple some of Drifblim's usual checks and let it avoid Sucker Punch, but outside of the accuracy issue, a Drifblim without a coverage move is walled by Normal-types and struggles even more against Dark-types. Since Drifblim may end up being unable to sweep the opposing team, Baton Pass ensures that all of the Calm Mind boosts accumulated won't be a waste if you pack another special attacker. Moreover, Baton Pass allows Drifblim to escape Pursuit. If Drifblim is holding a Petaya Berry, giving up Calm Mind is also possible, as it will free up a moveslot and let it use one of the above options or other offensive options like Thunderbolt and Explosion instead. Although it wouldn't have to set up manually with Calm Mind anymore, eating the Berry requires Drifblim to be at very low health, and it will only get a +1 boost in Special Attack by doing so, making sweeping difficult.
With Skuntank being Drifblim's biggest threat, Pokemon that can lure it out and either cripple or outright KO it like Gardevoir with Will-O-Wisp, Focus Blast, or Destiny Bond and Shiftry with Explosion make good partners. Other Dark-types with super effective priority moves like Shiftry and Cacturne are pretty annoying as well, although Substitute helps Drifblim against them. Therefore, having a good switch-in to most of them like Vileplume is appreciated. Specially bulky Pokemon with super effective coverage like Regirock, Cradily, Regice, and Muk need to be out of the way or severely damaged in order to sweep with Drifblim. Wallbreakers like Medicham threaten all of them. Another way to wear down said Pokemon is with Spikes and Stealth Rock support. Drifblim's Ghost typing is something to take advantage of against opposing spinners, although its weaknesses to Hitmonchan's Ice Punch and Sandslash's Night Slash make it a pretty subpar spinblocker. Even though Drifblim doesn't mind Stealth Rock that much, as it needs to get in Sitrus Berry's range anyway, Rapid Spin support from Hitmonchan or Sandslash is still appreciated, as Drifblim will likely have an easier time setting up if it comes in at full health. Moreover, both of these Pokemon are pretty good at checking most of Drifblim's threats, namely Regirock and Skuntank. Also, due to Unburden, most of Drifblim's answers are either strong priority users or specially bulky Pokemon. Nonetheless, naturally faster Pokemon can also pose a threat if they pressure Drifblim enough to prevent it from setting up. These include most special attackers like Haunter, Jynx, and Manectric. Thus, packing a special wall or tank like Lickilicky is a good idea.