Need help finding the CR on this "boss"

[Red_Death01]

So I'm still learning to DM like my friend and a challenge I still face is guessing the CR... The fight will be a 1v4. I plan to have the party reach him around level 5 or 6 and have a significant problem with him (though not a 80% chance of frozen death). The area he'll be fought in is on top of a large snowy mountain top and the characters will likely have suffered or staving off some form of cold environment (around 30F) to reach him. My GOAL was to hit a CR of 9 or 10

The Stats:
Ice Golem* --I used Ice Golem (from frostburn) as a basis
Large Construct (Cold)
Hit Dice: 12d10+30 (96 hp)
Initiative: -1
Speed: 20 ft. (4 squares)
Armor Class: 16, touch 8, flatfooted 16
Base Attack/Grapple: +9/+18
Attack: Slam +13 melee (2d8+5)
Full Attack: 2 slams +13 melee (2d8+5)
Space/Reach: 10 ft./10 ft.
Special Attacks: Ice shards, Unstable blizzard
Special Qualities: construct traits, immunity to cold and magic, vulnerability to fire
Saves: Fort +4, Ref +3, Will +4
Abilities: Str 21, Dex 9, Con —, Int 3, Wis 11, Cha 1
Challenge Rating: ???

Ice Shards (Su): As a free action once every 1d4+1 rounds, an ice golem can generate a spray of deadly ice shards from its body, dealing 2d6 points of piercing damage and 1d4 points of cold damage to all creatures within 10 feet.

Construct Traits: An ice golem has immunity to poison, sleep effects, paralysis, stunning, disease, death effects, necromancy effects, mind-affecting effects (charms, compulsions, phantasms, patterns, and morale effects). It is not subject to extra damage from critical hits, nonlethal damage, ability damage, ability drain, fatigue, exhaustion, or energy drain. Cannot heal damage normally.

Immunity to Magic (Ex): The ice golem is immune to any spell or spell-like ability that allows spell resistance. In addition, certain spells and effects function differently against the creature, as noted below. Fire spells and effects affect the ice golem normally, even if they permit spell resistance (but note the golem’s vulnerability to fire). Although it is not undead, the ice golem shares some vulnerabilities with the undead. It takes damage from positive energy even if the spells permit spell resistance, as if it were undead. The ice golem is immune to turn and rebuke undead. A magical attack that deals cold damage heals ice golem of 1 point of damage for each 3 points of damage such an attack would otherwise deal. If the amount of healing would cause the golem to exceed its full normal hit points, it gains any excess as temporary hit points.

Unstable Blizzard (Su): As an immediate action the ice golem causes the area he is within to begin to freeze instantly. Anywhere within 100 ft (20 squares) of the ice golem is treated as being in an Extreme Cold area. The ice golem can only use this ability should his health be equal to or lower than 50% of his maximum health. (Extreme Cold affects the ice golem however, damage taken will heal it instead.)


*To explain some of the strange additions:
Mainly the main antagonist (whom the party will be formally introduce to upon defeating this) has used some strange form of dark magic to convert a powerful warrior who lived in a house at the top of the mountain into a twisted monstrosity part undead, part elemental.

Any nitpicking, suggestions, or comments would be greatly appreciated.

> Edited to remove errors in stat block

[docnessuno]

I can see multiple errors:

Initiative should be -1
BAB should be +9
Slams should be +13 (9 BAB, +5 Str, -1 size)
Grapple should be +18 (9 BAB, +5 Str, +4 size)
Saves should be +4 / +3 /+4 (+4 base, -1 Dex for reflex)
Int 3 means the construct must select feats (5) and skills (15 points)

Monstrosity Traits: The vast majority of those are rendundant, being already covered by the construct type.

Vulnerable to Positive Energy: should be removed and the vulnerability added up in Immunity to Magic, no reason to have two separate entries.

Also i'd make some changes:

Unstable Blizzard: make it always active and reduce the range (10-20 ft). It's a flavourful ability and 1d6 damage / minute won't change much. I'd also add the ability to ignore ice-based difficult terrain and make the whole area slippery (as grease).

I'd also raise the AC by 2, 16 is really low for a melee boss.

Overall i'd rate it as a CR 8-9 (9 with Int, 8 if changed to midless), considering a clay golem (CR 10) has more strenght, DR 10 / good luck beating it, a much more restrictive magic vulnerability and the nasty cursed wounds.

[Red_Death01]

Thank you for the fixes!

What would be a good suggestion on feats to choose from?

As well as for the unstable blizzard I'd prefer it to affect everyone in the fight, otherwise I feel it'll be punishing melee fighters too much while the casters don't change their tactics at all.

[docnessuno]

Thank you for the fixes!

What would be a good suggestion on feats to choose from?

As well as for the unstable blizzard I'd prefer it to affect everyone in the fight, otherwise I feel it'll be punishing melee fighters too much while the casters don't change their tactics at all.

As it is, it probably won't affect anyone in the fight, unless it drags for 10 or more rounds (unlikely).

About feats, keep it simple but give him some combat options:
Improved toughness
Power attack
Improved bull rush
Knockback (use it in conjunction with chasms and other obstacles)
Shock Trooper (Don't use Heedless Charge to avoid 2-shotting your party, but the other two options are great)

With this feat selection, AC bumped to 18 and some terrain enabling him to knockback people into bad spots (chasm, difficult terrain, 10-20ft cliffs) i think the encounter CR could approach 10.

[Red_Death01]

As it is, it probably won't affect anyone in the fight, unless it drags for 10 or more rounds (unlikely).

About feats, keep it simple but give him some combat options:
Improved toughness
Power attack
Improved bull rush
Knockback (use it in conjunction with chasms and other obstacles)
Shock Trooper (Don't use Heedless Charge to avoid 2-shotting your party, but the other two options are great)

With this feat selection, AC bumped to 18 and some terrain enabling him to knockback people into bad spots (chasm, difficult terrain, 10-20ft cliffs) i think the encounter CR could approach 10.

Alright thanks! Greatly appreciate the help.

[docnessuno]

Also note that "vulnerable to X" means it takes 1.5x damage of that type, so remove the "vulnerable to posititive energy" SQ, unless you meant the thing to be even more vulnerable than undeads.
The fact that he can be harmed by it is already stated in the magic immunity trait.

[awa]

i feel like with no dr and ac so low this thing will be dead fairly quickly.
whats your party composition that can make a huge difference.
also will they know positive energy hurts it, being able to hurt enemies with mass cure spells is great for the action economy

compare a frost giant more hp more ac more damge more accuracy and a ranged attack.

actually that's something to think about no reliable ranged attacks and a 20 speed means this things going to be pretty easy to kite does it have an answer to the ranged party members just backing away and shooting it? Or worse flying and shooting it.

[Xervous]

if the party has any sort of near optimized melee character, this thing will vaporize.

[Red_Death01]

If I double the current speed to 40 (as its original speed was 30 and say it gets +10 movement speed for being on snow/icy terrain) would that solve the potential kite problem or simply give it too much maneuverability?

I'm also fine with giving it back its original "damage reduction 10/bludgeoning". (possibly make it a flat DR 10/-?)

On the note with dealing with ranged targets- well that is another story, I think having unstable blizzard going from the get go may help a little while reducing the range to 50ft so they're not being frozen so quickly.... As well as increasing the range on Ice Shards by 10 (to 20ft)... tho casters/range likely will be around the 35-60 area....

>Also I didn't intend positive energy to do 1.5x so I removed that part thx.

[docnessuno]

Well, i suggested i slight AC bump, but i'd refrain from giving it DR or a significantly higher AC (i'd stick to 20 max).

Most golems are a bane to blasters, this creature is the blaster wet dream (the most common energy type bypasses its immunity and it's even vulnerable to it!). Giving him too much physical defences would just exacerbate the need for such blaster.

As far as movement and kitability, being slow-moving works fine thematicly. Instead of increasin the movement speed i'd just make the terrain icy, either trought a creature ability or by design (giving it an appropriate ability to ignore it), so other characters would treat it as difficult terrain and/or risk falling prone (and that's why i suggested the grease-like effect in the first place).

[awa]

if you have its blizzard create concealment so like say creatures with in 10 have no problem. creatures 15 30 feet have 20% miss and creatures 35+ cant see it at all will reduce players ability to get to far away.

if it has a wind component that will also make it hard just to ping it to death as well as encouraging flyers not to just sit out of reach.

dr/Adamantine is the default for golems

making the ground slippery and allowing the creature to ignore said slipperiness should dramatically reduce peoples ability to kite the monster

alternatively forcing the fight in a fairly small room with a low ceiling will make attacking it from outside the monsters reach much more difficult.

[Phaederkiel]

you could also say that the creature has a permanent wind wall due to his blizzard. Or even dice if the storm deflects ranged attacks. say they throw a fireball, if that fireball explodes 15 feet off target, it will still hit the critter, but heavily endanger the party too.

I think it is weird that the critter has no weakness to fire or sonic.

[Red_Death01]

Concealment was an original idea behind the boss but, I wasn't sure how to go about implementing it and would it affecting everyone beside him be too harsh?. Since I was wanting it to be a slow hulking monster I think adding the terrain difficulty being icy (grease effect) around areas or rubble spewed across the map limiting movement greatly for the party but not him works best.... AC I can boost an additional point- weaknesses--- I'd rather not give it sonic but, it already has fire.