Ideas to make an adamantine horror not so strong?

[Quentinas]

In my campaign I created a quest for my party to free a mine from clockworks horror and the ideas was that the clockwor horrors were trying to make a stronger clockwork horror like an adamantine horror but not so much strong/broken for the spell like abilities. Depending on how the players go it will not have the full hitpoins (but at least half hit points) but now the problem is that I don't know how create a clockwork horror strong but not lethal as an adamantine horror.
The party is composed by a
Hengeyokai factotum/prestige class similar to a ranger
Gnoll duskblade
Lesser drow ranger /cleric /sword dancer
Lesser aassimar shadowcaster/ master of shadow
They are quite high as level for the normal horrors as they are at level 13 but i'm not sure if a normal adamantine horror is too much or no as they have nearly the 50% of chance to pass the saving throw of implosion . ANother problem i have is with disjunction of mordekaisen as they don't have an equipment to be destroyed for now
So i was thinking that disintegrate should remain but what about the other stats = More hit dice , different spells or what else? Or I use a platinum horror with maybe some class levels and disintegration as spell like abilty ?

[Fizban]

The party is composed by a
Hengeyokai factotum/prestige class similar to a ranger
Gnoll duskblade
Lesser drow ranger /cleric /sword dancer
Lesser aassimar shadowcaster/ master of shadow
Sounds like the Duskblade is the biggest damage dealer, but how much damage depends on what spells they have available and how much burst stacking they're doing- just Arcane Channel, or also Spell-Storing and Smiting and who knows what else?

They are quite high as level for the normal horrors as they are at level 13 but i'm not sure if a normal adamantine horror is too much or no as they have nearly the 50% of chance to pass the saving throw of implosion . ANother problem i have is with disjunction of mordekaisen as they don't have an equipment to be destroyed for now
So i was thinking that disintegrate should remain but what about the other stats = More hit dice , different spells or what else? Or I use a platinum horror with maybe some class levels and disintegration as spell like abilty ?
Unlike most higher level constructs, or just most in general, it has no DR, and unlike most "magical" monsters, it lacks any extra movement modes. Its defenses are just AC 28 and SR 22, so this party should have little trouble affecting it and burning through its 98 hit points. And being 4 levels above CR, they are supposed to defeat it easily, if it's alone.

The threat of the Adamantine Horror is essentially all in the SLAs, which is a problem because as written they're clearly inappropriate for CR 9, at least on the surface, but what to replace them with depends on what CR you want to land at, and what creatures you find reasonable for that CR. Disintegrate was reduced to 2d6/level, but note that the given caster level is 14th, so the damage may still be instantly lethal without adjustment. You could use a spell such as Antimagic Ray for temporarily shutting down all of a creature's magic items (if they fail a save), Wall of Greater Dispel Magic or Otilukes Greater Dispelling Screen for stripping buffs if they move through it, or Chain Dispel to immediately strip all buffs, or meta-Chain Dispel Magic to strip all buffs and attempt to suppress a pile of items, or just write an antimagic monster ability to do exactly what you want.

Since Disintegrate was originally save or die and Implosion affects no more than one creature per round, the only real difference is that Implosion requires no attack roll and has no damage on a successful save, in exchange for Short range (and +3 DC). Short range instant death abilities can be found at CR 9-ish with the Bodak's 30' death gaze at CR 8, but at a far lower DC and with the allowance of closing your eyes. Still, conceptually the problem is not with the results of Implosion, but rather the range of insta-kill Disintegrate and Disjunction in general.

The lower-grade horrors have Lightning Bolt effects which are most easily stopped with buffs and/or magic items, so the leader would fit well in a support role of stripping buffs. Metamagic'd SLAs (non-core in particular) are not a normal feature of creatures, so the char-op solution of chain'd Greater Dispel isn't really appropriate*, so there isn't really an easy solution to shutting down magic items without another custom ability. Leaving the spell DCs nice and high but limiting it to Disintegrate and Antimagic Ray could work, giving it Fort and Will targeting effects while the other horrors target Ref, but still no area solutions for fighting the party unless you're allowing single-Disintegrate cave-ins. Add Wall of Greater Dispel Magic which it maintains over every entrance to any room it's in (or give it a constant sphere [which doesn't affect its own Antimagic Ray]), and some DR, and that should be sufficiently threatening to be worth a couple levels of CR, without reaching the Beholders 3 spells per round CR of 13.

*If you would allows a Chain SLA feat on the other hand, giving the AH caster level 12 and Chained (normal) Dispel Magic looks a lot less crazy than 7th and 8th level spells.

[Quentinas]

Thanks Fizban for the advices and here I put some more information
No Spell storing weapon or smiting spell but arcane strike as feat. Spells are somewhat difficult as various magic is impeded
Magic impeded
Magic with descriptor Fire Water Acid Earth Light
Magic of Illusion with glamer or phantasm descriptor
Magic of Conujuration with summoning or calling for elemental creature and outsider

So while the duskblade do good damage even the shadowcaster can do big damage but lesser time for day as it has umbral touch (trasmitted by the shadow elemental) and curtain of shadow

The adamantine horror will not be alone but I can't be sure how many horror will be as it is a time race before he arrive in the battlefield. I think there will be at least 2 platinum horror so for the CR it should not be so much difficult except for the SLA that are troubling me.
As the battlemap is a mine the battle will probably in short range so i prefer removing implosion (which have an higher save and would kill instantly) rather than disintegrate that require an attack roll and is easier.
While if the party would optimize his tactic a wall of greater dispel magic would be quite useful , this party doesn't use many buff (mainly the shadowcaster on the shadow elemental (on which it has two permanent spell one of rary telephatic bond and the other of greater magic fang) and rarely the cleric ) so I think antimagic ray would be more useful even to prevent the shadowcaster or the cleric to cast spells on a failed save.
As it is a leader of other clockwork horror an Energy vulnerability (2 party member affected with each cast) maybe with the quicken spell like ability feat how would you see so the not so high damage of the other horrors would do more damage .
For the DR maybe 5 /adamantine would be good they don't have any adamantine weapon and if I put a 10/adamantine the factotum would have big problem at doing damage without inspiration