So, not necessarilly a core but vgc wise:
Mantine, Tapu Bulu, Decidueye, A-Sandslash, Passimian, Mudsdale
Mantine has received a great buff with roost and +20 bst hp and its types resist both fighting and fire, wich A-sandslash doesnt really dig. Decidueye and Bulu also enjoy having an ally with fire resistance and ice neutrality. Mudsdale will thank you for mantine's ability to come in on an ice attack and water immunity.
Tapu Bulu can take resisted fighting hits for A-sandy, electric ones for Mantine and Blocking the ever annoying Dragon moves, all while setting up grassy terrain to nerf earthquakes damage and cancel any weather damage the team could receive.
Decidueye can block unwanted normal and fighting moves and resist electric shots for Mantine while having the incredible utility Spirit Shackles offer along with quite a good support movepool.
A-Sandy has decent offensive typing with Ice and Steel while having quite a few good resistances. It can come in and laugh at ice (for bulu, decidueye and mudsdale), flying (Passimian), and dragon moves for it's team.
Passimian is a trump support brawler with an incredible ability that can come in and reset weather instead of bulu once it dies or acquire slush rush and outspeed most things. It can take some hits on its own with a little investment and can be a damn tank with mudsdale's ability. The one thing it lacks other than more coverage is entrainment (Gf, please i beg of you) but we can wait. Meanwhile it does get QuickGuard, Scary face, Beat Up (it is a pretty heavy hitting team to be fair. That plus beating up mudsdale with chesto resto equals awesome (if you get the chance, of course)), Rain Dance (swift swim mantine receiving), Smack Down, Acrobatics, Iron Head and Close Combat, Low Sweep, feint, all great moves for a support bruiser. He does have so many options its hard to chose.
Mudsdale brings an electric immunity to the table, along with a solid ability to check fake outs and physicall hits.
Something like
Mantine:
Water Absorb/Swift Swim
Leftovers, Sitrus, Lum
Scald
Roost
Wide Guard
Hail
Scald is quite obvious
Roost Because that's what it has allways wanted and I don't see it parting with it anytime soon now that it got it.
Wide guard for the obvious spread moves.
Hail to set up for sandslash if needed without having a setter with shared weaknesses with A-sandy (looking at you A-Ninetales).
Tapu Bulu:
Sitrus/grassy Seed/Leftovers/whatever your heart tells you to
Horn Leech
Protect
Nature's Madness
Bulk Up/Rototiler
Horn leech is for improved sustain and a nice boosted stab on grassy terrain.
Protect because VGC
Nature's Madness because this team has no Special Attacker and we need to break Sponges somehow, this should help.
Bulk Up for selfishingly buffing or Rototiler to buff Decidueye's Spirit Poke as well.
Decidueye:
Carefull/Sassy 252 hp, 120 def, 130 sp def, 4 speed(or whatever you want, honestly still gotta test this thing to tune it better)
Ghost Z-stone/Leftovers/grassy seed
Spirit Shackles
Roost
Curse
Protect/Low Sweep/feather Dance/Leaf Blade
Spirit Shackles Because thats what decidueye is all about.
Roost for recovering from enemies and curse damage more than just by items or grassy terrain.
Curse for the oportunities you get to curse someone that is shackled and still survive to roost away. (Probably those sponges we were talking earlier)
Z-curse for recovering full hp and assuring at least one shackled cursed mon in the game.
Protect because VGC [2] (if running leftovers, bonus heal), Low sweep for coverage, leaf blade for alternative stab with grassy terrain boost (but really, with bulu on the team thats all the grass you need). feather dance to debuff the enemies attack if you feel you actually need more staying power.
A-Sandy:
Icicle Spear
Iron head
Protect
Aurora Veil/safeguard/coverage move.
Aurora Veil for the same effect of double screens comming of a fast mon (Slush boost). Safeguard to avoid those unwelcome statuses, but mostly for burns. Coverage if you feel you need it.
Passimian:
if guts - Adrenalin Orb
Else - grassy seed/sitrus/lum/z-stone
Close Combat
Protect/Quick Guard
feint/rain dance/Beat up
Iron Head/Smack Down
Close Combat - because damage!
Quick Guard - its a slow meta, priority will still be a thing, even with all the nerfs. A-Sandy thanks you for no mach punchs
feint to avoid those pesky protects that would make spirit shackles fail and ruin decidueye's day. Z-boosted Rain dance for a speed boost and receiving Mantines swift swim or simply to counter weather. Beat up for gimmick setup of mudsdale and have a 1 turn +6 defense.
Iron Head - Because fairies are annoying and we don't get to play with poison jab =/. Smack Down for flying types with the added bonus that mudsdale can hit them with its stab after that.
Mudsdale:
Stamina
Chesto Berry
High HorsePower
Heavy Slam
Protect
Rest
High Horsepower to avoid self counter with grassy terrain.
Heavy Slam to get some awesome base power neutral damage since this horse is heavy as hell.
Rest to recover after receiving some physical damage and setuping a little.
I know it's an entire team but one can take what it does not want out and put in something that pleases one more. The thing is, I've not yet thought of anything (other than the obvious lack of special power) that would screw this team up entirelly.
It does well on trick room, it is tanky enough to handle being outsped, has more than one switch in option for each weakness that I could think off and does have a fairlly good damage output, considering it does have 2 mons that do not care about intimidate for damage (decidueye with curse and bulu with nature's madness), one special attacker (not invested thou) in mantine and one potencial guts user in passimian.
I am sure that I forgot to consider something (probably something obvious) so, any thoughts?