You're welcome.
Since I'm sitting around on a Saturday morning with not much to do I thought I'd add a few thinks. What can I say? It's a fun though exercise.
It occurred to me that wish can also be used to cast permanency. Don't worry about costs - draggy has that nifty ability to ignore those. So draggy should have all the good options (resistance, arcane sight, see invisible, greater magic fang (+5 hit and damage), tongues.)
Plus a few permanent lair defences like teleport trap (set to the lava, obviously, this will effect anyone trying to teleport/dim door to a point inside the lair, even if they're already inside the lair.)
Alarm (there's that excuse for pre-fight buffing, cast soooo many buffs.)
mage's private sanctum to prevent scrying,
walls of stone with phase doors to create a secure inner fortress.
Hell, draggy can have their own demi-plane. They'll need to use wish to enter it though... or a contingency plane shift.
Also the lair can be covered in all manner of Symbols. Like, almost all of them. They offer saves and draggy's spell DC is only average. But everyone fails on a 1.
Unhallow. nothing stopping draggy from using this. Either place in a choke point and link dimensional anchor to it. Or place it somewhere for draggy to make a last stand and link protection from energy (cold or sonic) to it.
Speaking of spells. Let's look at draggy's spell list.
As I mentioned in my first post I'm big on buffing. So I'm going to emphasise it as a strategy. (I know it's not the only way to go. But it's the best way.) Also, draggy doesn't have have high enough spell DCs to make spells that give saves much use.
level 1 - all good choices. You can swap out alarm for bless. I mean, it's cheesy for draggy to have to use wish to cast alarm but since they only do it once century or so, so why not? Bless is +1 morale bonus to hit.
level 2 - misdirection is pointless. I get it, draggy is meant to use it to hide their hoard. Well, they have a demi-plane for that now. Take Bull's Strength instead. +2 hit and damage. Alter self is only good for draggy to infiltrate humanoid society. Does draggy even care about that? If yes keep it. If not... mirror image is always cute. Or Bear's Endurance for moar hp (58hp.)
Level 3 - displacement - does everything greater invisibility does and less. Get rid of it. Draggy has quickened spell and needs something useful to do with it so I suggest lightning bolt. Quickened lightning bolt is a level 7 slot, they've got plenty of those. Tongues, once again, is only cast once a century or so using a wish. Try Prayer instead. +1 hit, damage, and saves.
level 4 - Stoneskin is pointless. Death ward is good as level drain is one of the few things that iron body doesn't protect against. Neutralise Poison is redundant - draggy has heal. Freedom of movement is nice but probably not necessary for draggy; not much gonna slow them down. Black Tentacles is cute but probably not stopping anybody (CMB of +24). I'm gonna suggest freedom of movement, just in case. Oh! Just thought of enervation. The PCs will be loaded down with fire protection but will they have negative energy protection? Plus it can be quickened for a level 8 slot.
Level 5 - greater command is crap. Everything else is good. Cloudkill is cute. CON damage is always fun. And it can be cast during time stop to take effect after the time starts again. Unless everyone is immune to poison. Teleport. I assume this isn't the sort of campaign where the villain escapes to come back another day. But if it is teleport is your friend.
Level 6 - all good.
Level 7 - mass hold person is a waste of space. It's DC is 23, piddling to these guys. Banishment. Dispel Good may not work, so this might be handy. Teleport greater for running away. Restoration greater in case the tricky buggers sneak anything nasty past your defenses. Otherwise good.
Level 8 - iron body is great. sympathy can be funny but the DC is only 24. Also is blocked by a simple protection from evil. replacements: Protection from spells if you feel draggy's saves aren't up to scratch. Dimensional lock is good for stopping them doing all that tricky extra dimensional movement stuff. Horrid wilting is ok. 19d6 damage, untyped so no DR. Greater spell immunity to be immune to 4 spells of 8th level or lower. (which 4 spells... polar ray? temporal stasis? polymorph any object? trap the soul?)
Level 9 - times stop and wish are good.
So to re-visit all those buffs I hope draggy has in place: they should have the following increases: +13 attack, +11 damage (+13 for the bite);* magic, adamantine and dragon bane attacks;+13AC ** (only +9 vs. non-good opponents); +6 saves/+7 reflex saves (only +2/+3 vs. non-good opponents) DR 15 or 20. Starting to look solid.
Another tactic that has occurred to me: the crush ability is a good way to pin a caster or 2. Casters who are pinned and taking damage aren't doing much. So on draggy's second action it might be worth using this instead of all the attacks. Which is better is going to depend on the situation.
Mage's Disjunction is gonna screw you if you fail a will save. Resistance, Prayer and Dispel Good should make draggy's will saves +31. Wish can be used retroactively to give you a re-roll. This should be sufficient to resist it.
I mentioned above about swapping out the vital strike feats . That gives you back 3 feats. Fly-by attack is important. Do you allow the leadership feat? If so give this guy a 20th level follower. Someone who can cast spells. If you allow PC classes then a bard or wizard who can ride on him. A dragon born obviously. Or a CR 22 dragon. Technically 'dragon' is not a PC class. If you've already got fly-by attack and combat reflexes why not add dodge and whirlwind attack to the mix? Not awesome but it allows draggy to use a bite attack on everyone in range if they're getting mobbed. And another +1AC. But if you allow leadership, take leadership.
* greater magic fang, bless, bull's strength, prayer, iron body, haste.
** shield, mage armour, dispel good, haste.
And to emphasise what Alzrius said: draggy should use any magic items they can.
Woo. I have literally spent my whole morning on this. Thanks! I've enjoyed it. Now I must away to my urban fantasy game.
Didn't buy that Colossal Red Dragon mini for nothing!
That's a hell of a mini. Hell, it's a maxi.