Pokemon: Ninetales
Type: Ghost/Fire
BST: 80 / 50 / 110 / 105 / 110 / 115
| 570 BST
Abilities: Poison Heal / Magic Guard / Drought
New Moves: Shadow Ball, Recover, Taunt
Niche: Fits flavour-wise. Now Ninetales is a fast mon that can take some hits from both ends of the spectrum , with Ghost/Fire providing 7 resistances and 2 immunities. Drought is a Ninetales staple (and hey two more immunities are nice switch-in opportunities). Magic Guard to prevent poison and hazard damage (and really fits with the kitsune thing) and Recover helps with the tanking. Poison Heal takes advantage of the fact that Ninetales is immune to burns, so the only passive status it fears (Poison) now helps it, although you lose hazard immunity from Stealth Rock and Spikes (which will get healed anyway). Taunt is also a nice tool with its speed and is helpful against stall teams. Otherwise, it also has Calm Mind/Nasty Plot to boost its Special Attack.
Pokemon: Dusknoir
Type: Ghost/Dark
BST: 80 / 120 / 135 / 65 / 135 / 35
| 570 BST
Abilities: Analytic / Dazzling / Oblivious
New Moves: Spirit Shackle, Recover, Knock Off
Niche: Let's try to buff Dusknoir yet again. Now with only 1 weakness to Fairy, it can be even more bulkier in general. Analytic makes use of its low speed for more offensive presence and can lead to powerful Paybacks. Oblivious makes sure it gets Trick Room up or doesn't get Taunted while using Recover. Spirit Shackle for a stronger Ghost STAB and it fits with the Grim Reaper thing. Dazzling might sound weird for a mon with such slow Speed, but this fixes the problem of Trick Room being susceptible to priority moves so it can be a self-sufficient Trick Room sweeper.
Pokemon: Muk
Type: Ghost/Poison
BST: 105 / 105 / 95 / 90 / 105 / 70
| 570 BST
Abilities: Levitate / Flare Boost / Gooey
New Moves: Spirit Shackle, Parting Shot, Recover
Niche: Pretend it upgraded to ectoplasm or something (or Ghostbuster's Slimer)! Levitate gives it 3 immunities which is nice for switch-ins. Flare Boost is a baiting Ability, for those who think they can neuter Muk's physical sets with a Burn. It has a decent array of special moves (Thunderbolt, Fire Blast, Shadow Ball, Focus Blast, Sludge Bomb) and Flare Boost doubles its Special Atk, so could be a fun set. Being a Poison-type means you (normally) can't be Poisoned, so why not use the Burn to your advantage? (Plus Flame Orb sets would mean you can't get be paralysed/asleep). Gooey is mostly for flavour, but you can also go for the Atk/Sp Atk/Spd drop combo with Parting Shot as you safely bring a frail mon in (having 2 immunities help with this pivoting support).
Pokemon: Marowak
Type: Ground/Ghost
BST: 90 / 80 / 160 / 70 / 90 / 85
Abilities: Sand Rush, Rock Head, Skill Link
New Moves: Rock Blast, Head Smash, Shadow Bone
Justification/Niche: Okay time to fix the last Marowak entry. This one is more of a physical bruiser Ghost type, with Onix-level defense (but you know, actually has offensive presence). Speed is average enough for outside Sand, but not too super fast when under Sand Rush mode. Shadow Bone for Ghost STAB, Head Smash for Rock Head and Rock Blast goes with Bone Rush for a Skill Link set.