i agree these cores are very good in dp nu
...regiking sounds pretty bad right now. it'd probably fall apart to most offensive threats. it's a REALLY outdated core lol. meditank is probably still great though because skuntank got some nice buffs this gen, but if you're going offensive on the dark-type, you should use drapion because it has knock off.
anyways i'm wondering how you guys handle escavalier (both avest and choice band). it's really fucking strong and hard to OHKO without a fire-type, and it can take advantage of so many good mons like reuniclus and shaymin. problem is, there isn't any particularly good fire-type right now aside from moltres. emboar is decent, delphox is decent, and then everything else is sort of bad.
Thanks for the feedback. To answer the first comment, only regiking was token from project NU lol, meditank was just a combo of a psychic trapper + a psychic lure that works extremely well in my experience. However, While regiking isn't great, both threats alone are great pivots into common threats, like regirock can pivot into things like Emboar and if equipped with a specially defensive or AV set, it can seriously wall a lot of things including things like Tornadus, Reuniclus, Kyurem and more. That being said it is a very outdated core, but I believe due to the low amount of wall breakers on most teams that seriously can beat this core, it can be effective, it just takes too much prediction and tip-toeing around certain wall breakers in order to be a threat alone, that being said Slowking and Regirock can be great pokemon ALONE as well if you put them to good use, so while they may not be the best core, they certainly are usable pokemon at the least (especially slowking, that thing dominated last gen and it might as well this gen)
In response to the Escavalier thing, this is what I have been using:
Moltres @ Leftovers / Life Orb
Ability: Pressure
EVs: 252 SAtk / 144 Spd / 112 HP
Modest Nature
- Roost
- Fire Blast / Flamethrower
- Hurricane / Air Slash
- Will-O-Wisp / Substitute
The purpose of this set is basically, to check Emboar, Escavalier, and well, it's moltres, it shits on lots of things so it's hard to explain in detail. Anyways, the EV spread outpaces jolly max speed Emboar and can Modest Hurricane it before it moves, the rest are clunked into HP and thrown into Special Attack for the sake of strength and bulk. This Moltres can equip either Leftovers for longevity or Life Orb for firepowe(puns :]). The moves are really a toss up, the only required one is roost, as without it, you cannot continue to check things so well for so long. The STABs are really power vs pp and accuracy, so whatever is more important to you, pick it. The last slot comes down to substitute for pressure stalling and subroosting or Will o Wisp for crippling physical foes that threaten to eliminate you, like AcroNadus. 
Moltres @ Leftovers / Life Orb
Ability: Pressure
EVs: 252 SAtk / 144 Spd / 112 HP
Modest Nature
- Roost
- Fire Blast / Flamethrower
- Hurricane / Air Slash
- Will-O-Wisp / Substitute
Here are some calcs to demonstrate it's effectiveness:
252 SpA Shaymin Seed Flare vs. 112 HP / 0 SpD Moltres: 46-55 (13.1 - 15.7%) -- possibly the worst move ever
252 SpA Life Orb Shaymin Seed Flare vs. 112 HP / 0 SpD Moltres: 60-71 (17.1 - 20.3%) -- possible 7HKO after Leftovers recovery
252 SpA Life Orb Shaymin Seed Flare vs. -2 112 HP / 0 SpD Moltres: 121-143 (34.6 - 40.9%) -- 64.6% chance to 3HKO after Leftovers recovery
252 SpA Shaymin Seed Flare vs. -2 112 HP / 0 SpD Moltres: 93-110 (26.6 - 31.5%) -- 29% chance to 4HKO after Leftovers recovery
252+ Atk Choice Band Escavalier Knock Off (97.5 BP) vs. 112 HP / 0 Def Moltres: 195-230 (55.8 - 65.9%) -- guaranteed 2HKO after Leftovers recovery(the second hit is not nearly as powerful, and you can roost up or just flame it's ass)
252+ Atk Choice Band Escavalier Knock Off (65 BP) vs. 112 HP / 0 Def Moltres: 131-155 (37.5 - 44.4%) -- guaranteed 3HKO
252+ Atk AV Escavalier Knock Off (97.5 BP) vs. 112 HP / 0 Def Moltres: 130-154 (37.2 - 44.1%) -- 100% chance to 3HKO after Leftovers recovery
252 Atk Choice Band Emboar Flare Blitz vs. 112 HP / 0 Def Moltres: 154-182 (44.1 - 52.1%) -- guaranteed 3HKO after Leftovers recovery
252 SpA Life Orb Yanmega Air Slash vs. 112 HP / 0 SpD Moltres: 169-200 (48.4 - 57.3%) -- 44.5% chance to 2HKO after Leftovers recovery
252 SpA Choice Specs Tinted Lens Yanmega Bug Buzz vs. 112 HP / 0 SpD Moltres: 116-138 (33.2 - 39.5%) -- 16.8% chance to 3HKO after Leftovers recovery
252 SpA Life Orb Shaymin Seed Flare vs. 112 HP / 0 SpD Moltres: 60-71 (17.1 - 20.3%) -- possible 7HKO after Leftovers recovery
252 SpA Life Orb Shaymin Seed Flare vs. -2 112 HP / 0 SpD Moltres: 121-143 (34.6 - 40.9%) -- 64.6% chance to 3HKO after Leftovers recovery
252 SpA Shaymin Seed Flare vs. -2 112 HP / 0 SpD Moltres: 93-110 (26.6 - 31.5%) -- 29% chance to 4HKO after Leftovers recovery
252+ Atk Choice Band Escavalier Knock Off (97.5 BP) vs. 112 HP / 0 Def Moltres: 195-230 (55.8 - 65.9%) -- guaranteed 2HKO after Leftovers recovery(the second hit is not nearly as powerful, and you can roost up or just flame it's ass)
252+ Atk Choice Band Escavalier Knock Off (65 BP) vs. 112 HP / 0 Def Moltres: 131-155 (37.5 - 44.4%) -- guaranteed 3HKO
252+ Atk AV Escavalier Knock Off (97.5 BP) vs. 112 HP / 0 Def Moltres: 130-154 (37.2 - 44.1%) -- 100% chance to 3HKO after Leftovers recovery
252 Atk Choice Band Emboar Flare Blitz vs. 112 HP / 0 Def Moltres: 154-182 (44.1 - 52.1%) -- guaranteed 3HKO after Leftovers recovery
252 SpA Life Orb Yanmega Air Slash vs. 112 HP / 0 SpD Moltres: 169-200 (48.4 - 57.3%) -- 44.5% chance to 2HKO after Leftovers recovery
252 SpA Choice Specs Tinted Lens Yanmega Bug Buzz vs. 112 HP / 0 SpD Moltres: 116-138 (33.2 - 39.5%) -- 16.8% chance to 3HKO after Leftovers recovery