Sometimes it helps to take a step back and look at what we do here:
The big question is whether the adept is really more powerful than the monk, as illustrated by and my monk build, both humans of 12th level; 25-pt-buy. (I listed the links to the builds again, because, strangely, for some reasons my build gets misquoted so often and confounded with a 7th level skill-focused monk build of mine that I think having the original links handy can only help the discussion ).
Firstly, the monk uses custom items that cast spells. 1st level spells at that. If this is allowed, I want a use activated sword of true-striking, and a use activated ring of divine insight.
It has been proven, multiple times. Why the dragon would fare badly against the adept without the lair. Attempting to snatch up the adept is close to impossible when he is in his army, also, the dragon would be using minutes to discern who is the threat through sense motive. The dragon probably don't have minutes unless it wants its' hoard stolen.
Well, I can use the White Dragon out of the box instead. However, the dragons that are described in MM are not complete builds. They do not have feats or spells selected for them. In which case I guess it will be allright to give them some? A mature adult white dragon should have 7 feats and 8 spells IIRC.
1a) Adept vs dragon
The adept very likely has no chance vs the dragon, even (and probably even because of!) his animal/zombie zoo.
Not backed up.
Exactly, the adept wont get the surprise round, the Dragon will use it's cave to deal with him. It will probably hide in a tunnel in the ceiling, due to it's permanent spiderclimb on icy floors. It's hoard will probably be frozen inside that same ceiling, like white dragons apparently prefer to.
Yes, the dragon now has 1.5 rounds to discern who is the threat. Something that by and large takes either 20 rounds for taking 20 on a spot check, or a minute for attempting a sense motive threat. It doesn't have the time for either, so it attacks randomly and have about 10% chance of hitting the adept.
Nope, but it does get the adept the ability to hide behind his zombies, or find some cover.
Even on a save the dragon is entangled by web:
And web works even better:
Each round devoted to moving allows the creature to make a new Strength check or Escape Artist check. The creature moves 5 feet for each full 5 points by which the check result exceeds 10. The dragon will not be moving more than 5-10 ft in the web each round.
All rounds in which the adept and his friends can use to let loose an artillery barrage against the dragon. Also,
Web offers no spell resistance.
Decent trick. I would probably just send in the Shadow and tell it to kill ANY dragon it finds inside instead of going in there with it. The dragon doesn't have much to deal with it except a few magic missiles, and if the polymorphed undead was a Hydra, it would have too many HP to kill with that. The adept could also have a Necropolitan under his control (who he could have commanded to become necropolitan when they had a cyst in their head). Who would be intelligent enough to search for the dragon.
The adept has, among his zombies multiple modes of movement. Getting them around might prove a small hurdle, but not that much. A clever dragon would use this in the fight though.
I think you misunderstand, the joker monk needs to spend those gold to keep being effective, he gets diminishing returns.
The adept, on the other hand, spends his money getting more and more zombies and followers. Increasing his power for every fight he does.
1b) Monk vs dragon
Even out of the box, the dragon can wreak that monk build. Even though it uses items that aren't allowed. Warning can't be put on an amulet, it is a weapon enhancement. You can't have items that can cast spells like that out of custom items. Custom items break the game in and on themselves.
He has stealth abilities. He could try an ambush somewhere outside the lair after observing the dragon for a while (the monk has ring of sustenance, he can take his time). Also, his knowledge-arcane skill may be useful. Also, his high spot and listen modifiers will help him not to be surprised by the dragon.
He can fly for a total of 25 rounds each day with his winged vest. How is going to ambush the dragon who flies faster than him at all? If the dragon met the monk outside, it could simply breathe frost at him and move to always be outside his range. If he decided to come closer, if he didn't activate his torc, the dragon could simply eat him. Or it could sunder his vest making him fall. The monk can only move 90ft in a charge while he is flying.
So he gets to make one attack at the dragon with his AoO, then activates blink. Then he loses his next swift action, so next round he can't activate his torc, meaning he can't trip the dragon. The dragon can just keep attacking him, hitting with one attack can mean the end for the monk, because the dragon could just grapple him.
Where are you getting enlarge again? Your custom item? Fine, you don't have that. Torc of the Titans is a swift action activation. You can't do that on an AoO. you are now at +13 against +20. Pretty hard to trip the dragon now, isn't it?
Well, You can't activate both the Torc and Heartseeker amulet. You don't have any source of enlarge. Fanged ring doesn't stack with INA. I'm at most getting your size to Huge here. That's not 24d6 of damage. The dragon has +17 Fort save, meaning he makes the save on a 4 or better. That is 15% chance per attack of failing. Giving the dragon around 75% chance of not being stunned. Assuming you don't fail on your own miss chance. Heartseeking amulet only works on one attack. So you only hit with one of your two attacks.
Note that things will definitely go wrong for the monk.
FTFY
Why not? He is hiding behind miss chances, he probably doesn't have a good AC.
It's not likely to work against the Adept either. Which has been pointed out multiple times
As soon as the dragon somehow does not manage to kill the monk before the monk gets to act twice (=four attacks for each 40ish-100ish damage, plus four DC 21-23 stuns), he has a problem. Note again how the adept needs 4 rounds (= scorching rays) to kill the dragon even in the most favourable of circumstances.
But it can quite easily kill the monk ridicolously fast. And why would it ever allow the monk to make full attacks against it?
Why wouldn't the dragon be flying? Sometimes it might be climbing on slippery ice slopes (read ceiling) instead. But you can't charge there anyway.
The adept has spells. And quite a bit of them.