The thread is filled with bad answers actually, I hope this one would be better than the others…
In ORAS Pure Hackmons (Gen 6 PH), I was experimenting with some Shadow Tag trappers, and I found out that a Stag Trapper + a Mold Breaker is an extremely efficient core, as they can slowly break down their own checks and counters, that also with relative ease.
Over here, I’ll be showcasing my dual-Gengar core, which is a pretty cool core and helped me get top 10 on the ladder (which apparently is nothing, but their success in RoomTours is pretty nice too).
Shadow Tag Gengar-Mega + Mold Breaker Gengar-Mega
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(Click on the sprites for an importable!)
This is a pretty solid core of two Gengars. Whenever one thinks of Mold Breaker Gengar checks, Wonder Guard Audino-Mega, Drapion (or Skuntank) and Arceus are the first Pokémon which come to the mind. These are, of course, the best checks to Moldy Gengar-Mega, so how can someone beat these Pokémon, paving a way for the Gengar to sweep? People think of other Molds and Huge Power abusers, especially Groudon-Primal and Mewtwo-Mega-X, respectively, but apparently, almost every team now incorporates at least two Wonder Guards, and of course the bulkiest Pokémon in ORAS Pure Hackmons: Giratina. The former dual-Wonder Guards cover almost everything that Huge Power Mewtwo-Mega-X can throw at them, and Giratina does the same as well as countering almost every set of Groudon-Primal. Therefore, with such a solid defensive core, a Gengar-Mega breaking without sufficient support would become a Herculean task. But we have arguably the most broken ability till Gen 6 with us, of course: Shadow Tag! With Shadow Tag + Perish Song, you can successfully trap every Wonder Guard without Shed Shell till you have Taunt and/or Encore. As STagSong abusers, Aerodactyl-Mega and Gengar-Mega’s are the premium Pokémon, because of their blazing speed, great typing and the ability to hold their respective Mega Stone. Why a Mega Stone? Mainly because of Trick. TrickChoice is extremely common here, as it can cripple almost every defensive WG and other defensive Pokémon too, by tricking a Choice item to them, limiting their overall usefulness. This is pretty cool for a STag + Perish Song abuser to have, as they’re deadweight with a Choice item. But other items like Safety Goggles are viable too, it’s choice in the end.
Now if we come to our core, we have two Gengar’s, a STagSong abuser and a Moldy Gar. Encore + Perish Song will force the opposing WG to repeat a move, and if you catch them with some move like Defog, you’re guaranteed with a dead WG. I like Spikes + Encore too, as you can simply set your Spikes easily with the aid of Encore, and then successfully trap the opposing Pokémon too, and the Moldy Gengar loves chip damage, so Spikes help it too. You can viably run Kings Shield than Spikes too, as then you can stall out turns easily, helping more in the Perish trapping. Recover is to recover off your health. The item is, again, changeable in accordance to what you and the team wants. The Moldy Gengar is a bit more straightforward, with the most common moves in Shell Smash, Judgment and Secret Sword. The last moveslot is free; you can run either Spore or Dark Void, depending on what you like more. Dark void has the niche of hitting even Safety Goggles users, but has a worse accuracy, whereas Spore can’t miss but can’t hit everything as the aforementioned Goggles are very common.
With the Shadow Tag Gengar trapping the most common checks of Moldy Gengar, the core works very efficiently, as in just a few turns games can change.
Aaah late edit but here's a team with the core!
Dual Gengar-Mega + AudPertTina Balance
(Click on the sprites for an importable!)
A pretty simple team build around the Dual Gengar core. I've explained what they do above, so I'll dive into the rest of the team now.
Audino-Mega + Swamper-Mega + Giratina covers legit every offensive threat in the metagame. Audino-M helps against Mewtwo-Mega-X, opposing Gengar-Mega and half the Mold Breakers. It's also a great Stealth Rocker and provides momentum with Volt Switch. Going for Volt Switch than any other pivoting move as the Gyarados matchup isn't very nice. Swampert-M is the second Wonder Guard and has a better matchup against Groudon-Primal and is a nice Defog user because of its resistance to Stealth Rock, and has a free moveslot to run Aromatherapy too. Thousand Arrows can be ran over Recover, but I prefer the longevity so I don't usually run that. Giratina is the bulkiest Pokémon in ORAS PH and for good reason too. It's a great Curse user which can stop Pokémon like mixed Groudon-P and Gear Grind + Leaf Blade Mewtwo-Mega-X right in their tracks without fearing anything from the in return (it takes like 40 from +2 Thousand Arrows from Groudon-P lol). We need Haze here as some Shell Shmashers are an issue, so it helps a lot. Now, I required some speed control and some more support, and so I went for Chansey, easily one of the only Pokémon to fulfil both these roles simultaneously. All in all the team's pretty nice and got me to 1702 ELO @ 89.7% GXE (W-L: 34-1), so I like it a lot.
Thats it, thanks for reading!!