Concerns regarding a new creature

[Alshoodone]

So recently I tried my hand at creating a new beast for the campaign I'm developing. I wanted something that was stationary, well-defended, but totally reliant on spells. The ending result is something called "The Grand Gem." My biggest concerns are the following:

- Can it just decimate an entire party without concern?
- Can 4 people just decimate it without a problem?
- Will it be challenging, or will it just gimp particular people?

The level the party is expected to be when they defeat this is 8, but they could also attempt it at level 9, as I don't level people for "Being somewhere that requires X" and use experience instead. The exact group hasn't been divvied out, but one can probably expect a Gunslinger, a Ranger (Not with favored enemy: Construct) a Witch, and a Frontline Cleric.

Here is the thing in all its glory.

The Grand Gem:

The Grand Gem CR 11
XP 12,800
The grand gem
N Huge construct (elemental)
Init +0; Senses darkvision 60 ft., low-light vision; Perception +18
--------------------
Defense
--------------------
AC 18, touch 8, flat-footed 18 (+10 natural, -2 size)
hp 131 (14d10+54)
Fort +10, Ref +4, Will +14
Defensive Abilities immovable; DR 10/—; Immune construct traits, critical hits, flanking, precision damage; Resist acid 5, cold 5, electricity 5, fire 5; SR 22
Weaknesses vulnerable to sonic
--------------------
Offense
--------------------
Speed
Melee unarmed strike +12/+7/+2 (1d6 nonlethal)
Space 15 ft.; Reach 15 ft.
Spell-Like Abilities (CL 14th; concentration +20)
. . Constant—detect magic, true seeing, truespeak[ARG]
. . At will—clairaudience/clairvoyance, make whole, stone shape, telekinesis
Sorcerer Spells Known (CL 14th; concentration +20)
. . 7th (3/day)—prismatic spray
. . 6th (6/day)—disintegrate (DC 22), greater dispel magic
. . 5th (7/day)—dismissal (DC 21), hold monster (DC 21), lightning arc[UM] (DC 21)
. . 4th (7/day)—greater false life[UM], phantasmal killer (DC 20), wall of fire, wandering star motes[APG] (DC 20)
. . 3rd (7/day)—fireball (DC 19), force punch[UM] (DC 19), slow (DC 19), wind wall
. . 2nd (8/day)—blindness/deafness (DC 18), flaming sphere (DC 18), glitterdust (DC 18), scorching ray, shatter (DC 18)
. . 1st (8/day)—color spray (DC 17), mage armor, magic missile, shield, stone shield[ARG]
. . 0 (at will)—acid splash, arcane mark, disrupt undead, flare (DC 16), ghost sound (DC 16), mage hand, mending, read magic, resistance
--------------------
Statistics
--------------------
Str —, Dex —, Con —, Int 18, Wis 18, Cha 22
Base Atk +14; CMB +16; CMD 26 (can't be tripped)
Feats Arcane Shield[APG], Empower Spell, Extend Spell, Focused Spell[APG], Heighten Spell, Reach Spell[APG], Toughness
Skills Appraise +18, Heal +18, Intimidate +20, Knowledge (arcana) +18, Perception +18, Sense Motive +18
SQ everlasting magic, magnificent formation, power overwhelming, reactive magic
--------------------
Special Abilities
--------------------
Arcane Shield Convert a level 1+ spell into + Spell Level deflection bonus to AC for 1 rd.
Construct Traits (+40 HP) Constructs have many immunities.
Damage Reduction (10/-) You have Damage Reduction against all attacks.
Darkvision (60 feet) You can see in the dark (black and white only).
Empower Spell Numeric effects of a spell are increased 50%. +2 Levels.
Energy Resistance, Acid (5) You have the specified Energy Resistance against Acid attacks.
Energy Resistance, Cold (5) You have the specified Energy Resistance against Cold attacks.
Energy Resistance, Electricity (5) You have the specified Energy Resistance against Electricity under specific conditions.
Energy Resistance, Fire (5) You have the specified Energy Resistance against Fire under specific conditions.
Everlasting Magic (Ex) A Grand Gem may cast Permanency for free, and at will, however it can only have 2 spells made permanent at any given time.
Extend Spell Spell duration lasts twice as normal. +1 Level.
Focused Spell You can cast a spell that gains +2 DC against one of its multiple targets.
Heighten Spell Increases spell level to effective level desired.
Immovable (Ex) The Grand Gem is completely immobile, and as a result is not able to be moved whatsoever. It is virtually immune to Combat Maneuvers. It is not immune to sunder, but its CMD against sunder attempts is equal to its current total AC. It is always considered flat-footed, but is immune to precision damage and critical hits alike. If it is ever forced to make a reflex save, treat its roll as though it rolled a natural 1.
Immunity to Ability Damage Immunity to ability damage
Immunity to Ability Drain Immunity to ability drain
Immunity to Bleed You are immune to bleed.
Immunity to Critical Hits You are immune to Critical Hits
Immunity to Death and Necromancy effects You are immune to Death and Necromancy effects.
Immunity to Disease You are immune to diseases.
Immunity to Energy Drain Immune to energy drain
Immunity to Exhausted You are immune to the exhausted condition.
Immunity to Fatigue You are immune to the fatigued condition.
Immunity to Flanking You are immune to flanking.
Immunity to Mind-Affecting effects You are immune to Mind-Affecting effects.
Immunity to Nonlethal Damage You are immune to Nonlethal Damage
Immunity to Paralysis You are immune to paralysis.
Immunity to Poison You are immune to poison.
Immunity to Precision Damage You are immune to Precision Damage
Immunity to Sleep You are immune to sleep effects.
Immunity to Stunning You are immune to being stunned.
Low-Light Vision See twice as far as a human in dim light, distinguishing color and detail.
Magnificent Formation (Ex) The Grand Gem adds its Charisma modifier to both its Fortitude and Will saves.
Power Overwhelming (Ex) A Grand Gem is a conduit of powerful magic. As a move action it can empower any spell it casts with one of the following metamagics, without increasing their spell level or casting time. Empower, Reach, Extend, Focus, or Enlarge metamagic. What's more, all of a Grand Gem's spells are treated as Silent and Still, without increasing their casting time or level, naturally. It cannot apply metamagic to spells above 5th level as a move action.
Reach Spell You can cast a spell with a range of touch, close, or medium as one range category higher.
Reactive Magic (Ex) The Grand Gem has Energy Resistances to all elements but Sonic, but as an Immediate action it can increase one of its resistances to 20. This lasts indefinitely, or until it changes the focal resistance to something else. It cannot protect against Sonic damage.
Spell Resistance (22) You have Spell Resistance.
Vulnerable to Sonic You are vulnerable (+50% damage) to Sonic damage.
Quick Casting The Grand Gem may cast defensively as a standard action.

It casts Extended Mage armor as soon as its time is up every single day, and has Shield permanent to raise its AC by 8, up to 26. It also has False Life, Greater on it permanently as well, but the health isn't evident of that.

It prefers to use immediate actions instead of swift ones to either change its resistance to spells with its Reactive Magic ability, or expend a spell with Arcane Shield to increase its AC even further.

[Ascalaphus]

It's got only a couple of long-range attacks - fireball, lightning arc, magic missile. Wouldn't the obvious way to handle it be to have an archer shoot it down from extreme range? With a composite longbow you could probably finish it off from the third range increment (staying out of range of all medium range spells) or from the ninth range increment (staying out of reach of all spells).

[Alshoodone]

It specifically has Wind wall to prevent that. It's encountered on a platform about 40 feet in the air with sheer cliffs on all edges.

[Bob Bob Bob]

Step 1: cut a hole in a box.
Step 2: put the gem in a box.
Step 3: repeat until it runs out of disintegrate.

More seriously, it's just a slightly monstrous sorcerer. I don't think you should use it though, as the CR is definitely wrong. Level 14 sorcerer is CR 13 to start, giving it extra abilities on top of that and an environment designed to favor it would increase the CR even more. Immobile doesn't really lower that unless the terrain is against it in some way (in a recess and can only see in a 90 degree cone, for instance). Full view of the battlefield and far away from enemies is the opposite of that.

It does have a few glaring weaknesses. As mentioned in the opening, anything that blocks line of effect shuts it down pretty hard. It autofails Icy Prison and presumably needs to disintegrate itself out. Then the players can shield themselves instead. Do the players have more 3rd level spells (Tiny Hut) than it has 6th (Greater Dispel Magic)? It has no healing so they can just trade fire with it, rest up, and come back and blast it again tomorrrow. Wind Wall is round/level, they can just leave and wait it out every time it pops back up. It's also useless against golems (though where players might get that, I don't know). I think all but glitterdust are SR:Yes? No quicken means readying to counterspell could completely shut it down (certainly long enough to throw a box over it).

For your questions:
No, it can't defeat a party. It can't stop them from leaving, it can't follow after them.
Yes, 4 people (with the right strategy) could easily defeat it. All of those strategies are fairly odd and incredibly "cheap shot"-ish, so most likely it won't be easy (except the archery one, that one might be obvious).
It will not be challenging. It will be frustrating and annoying. By far the best strategy is to shoot it, hide for two minutes when it uses Wind Wall, and repeat. For hours. Some of the spells seem malicious against certain character types too. Prismatic Spray basically only hits near the base of the platform. Ditto any short range spells. That's only the melee characters in the line of fire. And seriously, Color Spray? On a creature already 40 feet off the ground, that 15 foot cone is only good for things trying to melee it.

[Chromantic Durgon <3]

Like Bob Bob Bob said this isn't a challenge rating 11 creature and giving it a battlefield that works to it's advantage increases that further.

Also a lot of the strategies being suggested to deal with it are not what I'd expect a level 8 part to be running (spamming Tiny hut or Icy Prison for instance). It looks to me like you've designed an encounter that would be extremely difficult to deal with for any normal level 8 party to deal with fighting conventionally but not an encounter they can't escape from.

So that's what they're liable to do, retreat prepare a cheesy plan and then go cheese the shit out of it tomorrow. To me that doesn't sound like a lot of fun really just a frustrating thought exercise that encourages cheesy exploitation. Like an annoying raid boss.

[Alshoodone]

It's not 40 feet in the air. The players walk up and meet it on the platform. Also it can permanancy wind wall, can't it?

[Bob Bob Bob]

You know Permanency has an actual list of what's allowed, right? Wind Wall isn't on the list. For that matter, neither is Shield. If you give it the ability to make any magic spell permanent, that's way more powerful.

Alshoodone wrote:

It's not 40 feet in the air. The players walk up and meet it on the platform. Also it can permanancy wind wall, can't it?

Alshoodone wrote:

It specifically has Wind wall to prevent that. It's encountered on a platform about 40 feet in the air with sheer cliffs on all edges.

I hope you understand why this is confusing. So... is everyone on a platform, and that platform is 40 feet in the air?

Honestly, the longer I think about it the more I agree with Chromantic Durgon. They will notice it can't move and slowly plink away at it. If they realize it casts as a sorcerer (and therefore needs 8 hours of rest) then they'll get the martial to stay up all night harassing it (where can it go?) and make sure it doesn't recover spells. But it won't be fun. It'll be a long, slow slog.