Mostly Core big critter (Constructive criticism welcome)

[Xion_Anistu-san]

I have a short, one-shot Core-mostly campaign I'm creating and came up with a big critter for an encounter that I put before you for perusal and critique. This is for a brackish swamp/ bayou encounter with a group of 4 to 7 Level-7 characters. I'm going for a "What??!?" reaction from the party as well as a mid-point "Holy!! Look at the size of that thing!!"

The Black Wyrm

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                     Huge Dragon (half-dragon/constrictor snake)
Hit Dice:            12d10+50 (140 hp)
Initiative:          +4
Speed:               20 ft. (4 squares), climb 20 ft., swim 20 ft.,
                     fly 40 ft. (average)
Armor Class:         23 (-2 size, +4 Dex, +11 natural), touch 11,
                     flat-footed 18
Base Attack/Grapple: +9/+26
Attack:              Bite +18 melee (2d6+11)
Full Attack:         Bite +18 melee (2d6+11)
Space/Reach:         15 ft./10 ft.
Special Attacks:     Breath Weapon (DC21, 6d8), Constrict 1d8+11,
                     improved grab
Special Qualities:   Darkvision, Immunities (see below), Low-
                     light vision, Scent
Saves:               Fort +13, Ref +12, Will +7
Abilities:           Str 32, Dex 19, Con 20, Int 8, Wis 16, Cha 8
Skills:              Climb +23, Hide +15, Listen +22, Move 
                     Silently +19, Spot +22, Survival +7, 
                     Swim +22
Feats:               Extra Exhalation, Improved Initiative, 
                     Improved Natural Attack (constrict), Power 
                     Attack, Shape Breath
Environment:         Warm forests/ marshes
Organization:        Unique
Challenge Rating:    7

Combat
The Black Wyrm hunts by grabbing prey with its powerful bite and then squeezing with its powerful body.
Special Attacks:
—Constrict (Ex): On a successful grapple check, The Black Wyrm deals 1d8+11 points of damage.
—Improved Grab (Ex): To use this ability, The Black Wyrm must hit with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can constrict.
—Breath Weapon (Ex): The Black Wyrm has an acid breath weapon usable twice per day (once for half-dragon and once for the Extra Exhalation feat). Reflex DC21 for half, 6d8 points of damage. This is either in a 60 ft. line or a 30 ft. cone (as per the Shape Breath feat). It must wait 1d4+1 rounds between breaths or 1d4+2 rounds if it shaped its breath.
Special Qualities:
—Darkvision out to 60 feet and low-light vision.
—Immunity to magic sleep effects and paralysis effects. The Black Wyrm is also immune to acid because of its dragonic heritage.
—Scent (Ex): The Black Wyrm can detect opponents within 30 feet by sense of smell. If the opponent is upwind, the range increases to 60 feet; if downwind, it drops to 15 feet. Strong scents, such as smoke or rotting garbage, can be detected at twice the ranges noted above. Overpowering scents, such as skunk musk or troglodyte stench, can be detected at triple normal range.
Movement:
The Black Wyrm has the following modes of movement (other than walking and running):
—Climb: The Black Wyrm has a +8 racial bonus on all Climb checks. It must make a Climb check to climb any wall or slope with a DC of more than 0, but it always can choose to take 10 even if rushed or threatened while climbing. The Black Wyrm climbs at the given speed while climbing. It cannot run while climbing although it retains its Dexterity bonus to Armor Class (if any) while climbing, and opponents get no special bonus on their attacks against it while climbing.
—Fly: The Black Wyrm can move through the air at the indicated speed if carrying no more than a light load. (Note that medium armor does not necessarily constitute a medium load.) All fly speeds include a parenthetical note indicating maneuverability, as follows: average meaning it can fly as adroitly as a small bird.
The Black Wyrm can use the run action while flying, provided it flies in a straight line.
—Swim: The Black Wyrm can move through water at its swim speed without making Swim checks. It has a +8 racial bonus on any Swim check to perform some special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. The Black Wyrm can use the run action while swimming, provided it swims in a straight line.

Too powerful? Not challenging enough? What do you think?

[BisectedBrioche]

I like it. Although if its supposed to be a unique creature perhaps you should give it some fluff or back story?

[Xion_Anistu-san]

Thanks.

I'm working on the fluff as we speak. I wanted to make sure the mechanical end of things was good to go before I bothered to work on the fluff at all.