National Dex UU is the only format where Pursuit and Poltergeist are compatible, and where it can put in the slightest amount of work for a team.
Spiritomb @ Black Glasses / Sitrus Berry / Choice Band
EVs: 252 HP / 252 Atk / 4 SpD
- Sucker Punch
- Burning Jealousy / Will-O-Wisp / Trick
Poltergeist is your main STAB move. It reveals the enemy's item and does a ton of damage. Pursuit traps Pokemon like Mew and Slowking as well as Pokemon with pivoting moves like U-turn Urshifu Rapid-Strike style and Volt Switch Zeraora. Sucker Punch is nice priority.
Before you downvote because Burning Jealousy is here, hear me out. Spiritomb heavily relies on Dark and Ghost type moves as its main damage output. This means any Dark type that has bulk will be able to switch in (for example, Bisharp). Some Pokemon have the ability to stomach a potential Poltergeist, and then set up without being revenge-killed by Sucker Punch, or they have the ability to force it out.
These Pokemon include Urshifu-RSS, Aegislash, Buzzwole, Mega Altaria, Dragonite, Porygon2, Scizor, and Galarian Zapdos. Notice a pattern here? All these Pokemon have the ability to set up with either Swords Dance, Bulk Up, Dragon Dance, Curse, or Download.
You can make a risky prediction and stay in on these threats. However, scouting the set is very important. Who knows, you might use Burning Jealousy on Urshifu-S only to find its a Choice Band variant. Or that Aegislash you decided to stay in on? Instead of being Swords Dance, you find out its a Sub+Toxic variant.
Burning Jealousy allows you to push some chip damage, slight as it may be, on several targets, even if you don't predict correctly. Most notably, you can potentially 2HKO Bisharp and Curse Scizor after Stealth Rock, something which Poltergeist fails to do.
Burning Jealousy needs to be used in conjunction with skilled predictions, while Will-O-Wisp is fairly simple in its approach, but predicting correctly and getting a guaranteed burn on something setting up is better than accidentally missing Will-O-Wisp and giving the opponent a free turn to set up.
Trick should be used only on Choice Band sets. It can cripple several standard defensive Pokemon in the tier.