Lots of good insight, thank you. I'm typing on a tablet, so I'll keep the responses brief.
Here's my assessment, fwiw
Detection: A base +46 hide (+range), +50 move silent then paired with Shadow, basically means they better bring (widened?) Daylight, Luminous Armor, Blindsight 90+, or similar, or they're probably screwed at detection to even land a successful listen check to glitterdust. Presumably Mindsight isn't going to cut it due to mind-affecting immunity. If they don't get past this, it's probably a lose/draw.
The spotting through the invisibility is a great point. I'd not even thought of it. They will be bringing Daylight, and they have fought Shadow Creatures before, to great frustration.
Interesting point about the mind-affecting immunity possibly making him immune to mindsight. I'll have to look into it more, though I don't think it works like that, as I'm pretty sure you can detect undead with it. I'll look it up before the game tomorrow.
That's where the Hound comes in. If they then get hit by its Dimensional Anchor bite, they're probably no longer getting away (draw) to re-prepare.
The bite's effect is only for one round, and they are having an opportunity to break and prep at the start of the next session. A good point, but I think they will be alright. I'm mostly planning for them to face the one hound alone. Then the Hunter alone. A pack along with him would be too difficult.
Barb/Dusk: Should be able to at the very least True Strike Power Attack for damage. No problem.
Believe it or not, he doesn't have power attack. He does have Arcane Strike, however, and there was a lot of hinting from their Ghaele ally that the Druid NEEDS to prepare Brilliant Aura, to give them all brilliant energy weapons.
Druid/Sorc: Better have True Casting and Force/Sonic or no save/sr autosuck, or enough buffed damage in Poly/WS. My own PCs sorcerer would do Fusion: TC + Wings, and then soak with Wings of Cover, though if they remain flat footed against the attack...
The Druid is my hardest hitting striker, when he decides to get business done. He wildshapes into a tiger, casts Girallon's Blessing, dumps a spell into Arcane Strike, and charges for seven attacks, with each one getting +X to hit and +Xd4 to damage. He may or may not think to prepare Assay SR, but the Ghaele has said he is, so he hopefully got the hint.
Rogue/Wiz: MoTH has enough Spot to probably foil Invis/Hide as a means to SA. Same casting challenge.
Very good point, but I'm pretty sure he has been keeping his stealth skills up, so he might be alright. Also, due to circumstances, he doesn't have his full spell book, but has lots of things in his mind, uncast. He will probably be making a lot of use of his Acidic Splatter reserve feat, which doesn't allow SR, and the Hunter is not resistant to acid.
Actually, his invisibility would still be effective as far as denying the Hunter's Dex to AC. From the DMG section on invisibility:
"A creature can generally notice the presence of an active invisible creature within 30 feet with a DC 20 Spot check. The observer gains a hunch that “something’s there” but can’t see it or target it accurately with an attack. A creature who is holding still is very hard to notice (DC 30). An inanimate object, an unliving creature holding still, or a completely immobile creature is even harder to spot (DC 40). It’s practically impossible (+20 DC) to pinpoint an invisible creature’s location with a Spot check, and even if a character succeeds on such a check, the invisible creature still benefits from total concealment (50% miss chance)."
So, he's still invisible, the Hunter would just know what square he is in. The DC for this while the Wizard is active & attacking would be 40 (pinpointing an active invisible creature's square). That's just the base DC. The Rule's Compendium clarifies that the invisible creature's Hide check adds on top of that. And the way the Hide skill works, invisibility gives you a +20 bonus when moving around (it's fairly obvious this is supposed to be the source of the base DC of 20, but that isn't actually stated anywhere, so RAW it should add in too. Actually, maybe they are different things; the base DC for holding still is only 30, but the Hide skill says invisibility gives you +40 if you are immobile).
So an invisible, hiding rogue is at 1d20 + ~20 modifier + 40 = 61 - 80 as the DC to locate his square, and this is the hide check with the -20 sniping/attacking penalty that basically counteracts the +20 bonus from invisibility. So long as the rogue is trying to hide, on average he'll still beat the Hunter's average check result of 55.
Nothing seems to indicate the invisibility can just be ignored.
Rogue/Fighter: Probably going to have to rely on flanking to do any damage? Won't be able to PA/damage reliably against that AC/DR? Can he even keep up with the movement?
If Brilliant Aura or Brilliant Blade are in play, that will help a lot. His to-hit numbers are in the realm of +24, but higher if he's AoO'ing. Keeping up with the Hunter could be the big problem, though. You are right there.
Actually, he might be alright, if I steer the druid's spell choices a bit. The Rogue//Fighter will be Polymorph Other'd into a
gloura, so that with a Cloud Wings spell would give him a fly speed of 90 feet, which matches the speed of the hunter (90 ft due to shadow creature).
Fly 60 perfect or 240 phantom steed riding kiting, hard to detect with Total Freedom. The steed can give away the MotHs location, but it could also be used as a decoy to lure out the PCs.
Offensively the MoTH is going to ignore the spellcasters concealment buffs, but mirror image remains decent. So that may be rude surprise. It'll be a close check whether or not the MoTH can see through the PCs invisibility with its +45 spot check and at range.
Why would the Master of the Hunt be able to see through their concealment buffs? I may not have mentioned it here, but this is happening on the plane of shadow, so there is no moon, so many of his abilities do not function.
I'm drawing a blank as to what you are referring.
Once revealed, the MoTH could use it's Phantom Steed Ride/Cover to block attacks, if it continues at ranged, with quite a range advantage.
I hadn't even thought of mounted combat. That is so true. Granted, in most such instances it will "kill" the phantom steed, but he can just make a new one as a swift action, and he can fly on his own, so he won't fall out of the sky.
However, it's just as easy to drop a Forcecage on the guy (once detected). Don't know if you're giving him a get out of jail item or such to deal with this sort caster i win situation.
I am not giving him such an out. As a Shadow Creature he can Plane Shift 1/day, but he has already used it to come to the plane of shadow. The PC's have also asked the Ghaele to prep a few Dimensional Anchors. That along with Assay SR should help.
Now, if they've had a few rounds of fighting Shadow creatures previous, and KNOW they should be prepared for these types, it is their own failure to not be prepared for this situation. My PCs have had to learn the hard way about Protection from Evil diligence when they know they're fighting Vampires, etc. So, if they're vets at this point, I think its fair to put it on them.
They have fought Shadow Creatures before, though the fact they are currently on the plane of shadow has presented some additional problems (halved light radii, Spellcraft check required to even cast [fire] or [light] spells.) They are keying into some other tactics that will help, though. Getting Darkvision on everyone will be a big help in allowing them to sneak up to the location, for one.