I want to get this out there. I want to narrow our options a bit.
From what I collect, Ghost is virtually a manditory type here. Ghost is a magnificent type if a good Pokemon has it. It has 2 important immunities, a now-important Bug Restance, and a not-so-important Poison resistance. It only has Ghost and Dark Type weaknesses.
Now, what does this mean? Normal and Fighting are two moves that avoiding saves you a lot, you're not taking Dynamicpunches from Machamp, avoiding Lucario Aura Spheres, and stopping Focus Punch, Explosion, and Rapid Spin in their tracks. These are all common moves, and the most prevalent of them is DynamicPunch and Explosion. Ghost's Bug resistance and Fighting immunity bring it to Bullet Punching, and Will-O-Wisp (something virtually every Ghost carries) brings Scizor, and many other Physical pokemon, to a screeching hult. Rest is a common thing on Bulky Offense, but thats assuming that they're Sleep Talking will get them anywhere. If you can still 3HKO them, you're posting what will probably be too much of a feasible threat for them to do much, unless its like, Crocune with 6 CMs up. lol.
Ghost also hits the following Types, and the notable Pokemon in those types:
Psychic- Celebi, Latias, Starmie
Ghost- Dusknoir, Rotoms
STAB Ghost aint half bad is it? It covers a few IMPORTANT things reliably, doesn't it? Really, I think theres little arguement here that Ghost shouldn't be part of the typing, besides, there are never enough Ghost Types.
So, our two Main Ghost Ideas are Water/Ghost and my own Ghost/Steel. Lets just statisicamafy these guys.
Water/Ghost:
Weaknesses: Electric, Grass, Ghost, Dark
Resistances: Fire, Water, Ice, Steel, Poison, Bug
Immunities: Figthing, Normal
Normal: Flying, Psychic, Rock, Dragon, Ground
Ghost/Steel:
Weaknesses: Ground, Fire
Resistances: Grass, Ice, Flying, Psychic, Bug(1/4), Rock, Dragon, Steel
Immunities: Fighting, Normal, Poison
Normal: Ghost, Dark, Electric, Water
Noticable difference. The huge difference? No Dark Weakness here. I hate Pursuit weaknesses. They suck. So, we either go with the no-weakness Dark combination, or the resitance-bearing Steel. I chose steel.
But lets see how we do on the offensive.
Water/Ghost:
Super Effective STAB: Fire, Ground, Rock, Ghost, Psychic
Not Very Effective STAB: Water, Grass, Dragon, Dark, Steel
No Effect STAB: Normal
Normal STAB: I'm not doing this because I'd have to Color Code this HUGE list, and I'm waaaaaaaaaaaay to lazy for that.
Ghost/Steel:
SE STAB: Ghost, Psychic, Ice, Bug
NVE STAB: Steel(1/4), Electric, Water, Fire, Dark
No Effect STAB: Normal
Normal STAB: Same as last time.
If I bothered making the Normal STAB lists, you'd see that Water/Ghost hits slightly better than Water/Steel by a decent Margin, just like how G/S resists better than W/G by a margin.
What does this all mean? We have two VERY equal types here. They're all countering the same things, and all theoretically accomplishing equal jobs, just my Ghost/Steel is in a slightly more doing the job of stopping SE, or hopefully, even NORMAL effective damage being dealt from quite a few Bulky Pokemon.
Ghost/Steel Explanaiton support fun time!
Non HP-Fire Celebis are dead. You can freely switch in on Explosions and Draco Meteors. Most of the water Types are stuck at Surf, HAX Togekiss and Jirachi tend to not carry SE, or even NORMAL effective moves. And with Ghost's ironically perfect STAB going around, bulky offense either gets resisted or cries.
Some problems though, are Heatran, TTar, and Metagross. Nothing can be done about Metagross, and ONLY 4X moves can remedy Heatran and TTar (If you can outspeed them, of course, or catch them on the switch). Ghost/Steel has its holes, and it has instances where a bulky offense it could NORMALLY counter, has a way to beat it. But this is obviously said for any Pokemon....
Now, one more thing...
Toxic resistance and SR resistance are two things that makes Bulky offense harder, without Toxic (Spikes) or Stealth Rock helping them much. This is why Steel is such an amazing Anti-Bulky offense type. Spikes is the worst thing you can switch into, well, for field effects at least... Another great thing is Sandstorm resistance, which lets you keep your Leftovers until Abomasnow walks in.
I only see one REAL flaw with my typing, and thats a weakness to the ever Omipresent EQ. Fire doesn't scare me as bady seeing as you're top 3 Fire-using Bulky offenders IIRC, are Heatran, Celebi, and Latias. 2 of which are HP Fire. This pretty much leaves outside of that, Electivire's various Fire moves, some random Fire Punchers, and Infernape? EQ (and to an extent, Earth Power) is MUCH more of a threat. EQ is carried on a crapload of things, some of which Bulky offense. The only thing here is if you're faster, you can hope Will-O-Wisp hits, and if you're slower, either switch out or use a move in your arsenal that can take the Pokemon in question down if you have it. Earth Power is pretty much onl going to be seen on Heatran, which will probably be using Lava Plume, Flamethrower, or Fire Blast instead. Again, this is only remadied if Ghost/Steel is ever givena Ground move, and likely that will be no more than HP Ground.
Yeah... Thats really it... I'm not doing water/Ghost because I'd give it negative Bias, so, I'll let you get on that ^.^