Styx dragon 
HD: D12| Level | BAB | Fort | Ref | Will | Feature |
| 1 | +1 | +2 | +0 | +2 | Stygian Body, Styx adaptation, Fog Cloud |
| 2 | +2 | +3 | +0 | +3 | Keen senses, Stygian Breath |
| 3 | +3 | +3 | +1 | +3 | Blindsense 60 feet, Strength +1, Constitution +1 |
| 4 | +4 | +4 | +1 | +4 | Curse Water, Summon from the Deeps, +1 Charisma |
| 5 | +5 | +4 | +1 | +4 | Improved Breath weapon, Improved tail blades |
| 6 | +6 | +5 | +2 | +5 | Deeper Darkness, Stinking Cloud |
| 7 | +7 | +5 | +2 | +5 | Constrict, Improved Snatch, Diseased tail blades |
| 8 | +8 | +6 | +2 | +6 | Growth, Mind Fog, Feeblemind, +1 Charisma |
| 9 | +9 | +6 | +3 | +6 | Stygian grab, +1 Strength, +1 Constitution |
| 10 | +10 | +7 | +3 | +7 | Improved breath, Hold Monster |
| 11 | +11 | +7 | +3 | +7 | Stygian Scales, Stygian Influence, Stygian Corruption |
| 12 | +12 | +8 | +4 | +8 | Frightful presence, Growth, Crush. |
| 13 | +13 | +8 | +4 | +8 | Bonus Feat, +1 Charisma |
| 14 | +14 | +9 | +4 | +9 | Stupefying breath, +1 strength +1 Constitution |
| 15 | +15 | +9 | +5 | +9 | Disease ascension, Bonus Feat |
| 16 | +16 | +10 | +5 | +10 | Horrid Wilting, Corrosion, +1 Charisma |
| 17 | +17 | +10 | +5 | +10 | Stygian bite +1 Strength, +1 Constitution |
| 18 | +18 | +11 | +6 | +11 | Bonus Feat, Diseased Body, +1 Str, +1 charisma |
| 19 | +19 | +11 | +6 | +11 | Growth, Tail Sweep, +1 strength, +1 Constitution, Pestilence |
| 20 | +20 | +12 | +6 | +12 | Disease perfection, Bonus Feat, +1 Str, +1 Cha, +1 Con |
6 Skill points+int per level, quadruple at 1st level. Class skills: Concentration, Jump, Spot, Listen, Appraise, Bluff, Intimidate, Knowledge(any), Spellcraft, Swim
Proficiencies: a Styx dragon isn't proficient with any armor or weapons, besides his own natural weapons
Features:Stygian Body: The Styx dragon loses all other racial bonuses, and gains Dragon traits (60ft Darkvision, low light vision, and immunity to sleep and paralysis) plus the aquatic subtype. It is a dragon with a Bite 1d8 damage, 2 tail blades for 1d8 damage each, (They are secondary attacks and both are seperate attacks) a 40 foot base land speed which starts increasing by 10 every hit dice after its fourth and medium sized. In addition, the Styx dragon gains a swim speed equal to the base speed, and a burrow speed equal to half the base speed.
The tail blades only add your strength modifier to damage until level 5 at which point it becomes 1 and a half strength modifier
The Styx dragon's arms are vestigial and cannot be used for any purpose.
The Styx dragon also gets a natural armor bonus equal to 1+Constitution modifier. Whenever the Styx dragon grows one size category, his natural armor increases by a further 1.
Styx Adaptation:Ex The Styx dragon has complete immunity to poisons and diseases, magic or mundane. In addition, the dragon can breathe in water, Is not hampered in combat by being in an aquatic environment, and is immune to the harmful effects of the river Styx and cannot be affected by the disease ascension or disease perfection abilities of other Styx dragons.
Styx dragon SLAs: Any DCs are 10+1/2 HD+Cha mod.
At 1st level Fog Cloud SLA 2/day per HD. Any fog SLAs work underwater, producing a dark miasma instead of an usual cloud.
At 4th level Curse Water SLA 2/day per HD.
At 6th level Stinking Cloud and Deeper Darkness 1/day per HD.
At 8th level Mind Fog and Feeblemind 1/day per 2 HD.
At 10th level Hold Monster 1/day for each 5 HD.
At 16th level Horrid Wilting 1/day for each 4 HD.
Keen Senses:Ex At second level, the Styx dragon's senses become far stronger. The Styx dragon sees four times as well as a human in shadowy illumination and twice as well in normal light. It also has darkvision out to 120 feet
Stygian Breath:Su At second level the Styx dragon gains a breath weapon. The breath weapon is a 60 foot line dealing 1d6 acid damage/HD, with a reflex save DC of 10+1/2 HD+Constitution modifier for half and takes 1d4 rounds to recharge. The line increases by 10 feet for every extra hit die the dragon gains. In addition, at 5th level the damaging effects of the line cling to enemies. The next round the acid deals half the damage it dealt the previous round. At tenth level it affects them again dealing one quarter the damage it originally dealt.
Blindsense:Ex At third level the dragon gains Blindsense as the normal ability, range 60 feet.
Ability increase: The stygian dragon gains
+1 Str at levels 3, 9, 14, 17,18, 19, 20
+1 Con at levels 3, 9, 14, 17, 19, 20
+1 Cha at levels 4, 8, 13, 16,18, 20
For a total of +7 Str, + 6 Con and + 6 Cha at level 20.
Summon From the Deeps:At 4 HD the Styx dragon can use Summon Monster Y as a standard action, where Y it's half the Styx Dragon's HD, as a SLA 1/day per HD.
Creatures summoned this way have a swim speed equal to their best speed and gain the Styx Adaptation ability. If they already had a swim speed it is doubled.
Diseased Tail blades:Ex At seventh level anybody who is hit by the tail blades must succeed on a Fortitude save equal to the Dragon's breath weapon save or contract a disease of the player's choice. The player must choose once he gets this ability and the ability cannot be changed after this. There are several diseases on Page 292 of the dungeon master's guide or they can choose Stygian wasting from Draconomicon.
Improved Snatch:at 7th level the Styx dragon gains the Snatch and improved Snatch feat regardless of whether or not they meet the prerequisites.
Constrict: At seventh level, after the Styx dragon makes a successful grapple check, it can make a constrict attack. The constrict attack deals twice the tail blade's damage as bludgeoning damage.
Growth:At 8th level the Dragon grows to large size. At 12th he grows to huge and at 19th he grows to gargantuan. His AC, bonus to hit, base damage, grapple and skills change accordingly, but he doesn't get any ability score bonus or penalties.
Stygian Grab:Ex At 9th level the Styx dragon gains the improved grab extraordinary ability. To use this ability a Styx dragon must hit an enemy that is at least one size category smaller than him with his tail blades attack. The dragon can immediately make a Grapple check and if it's successful can use it's constrict ability in the same turn. In adition, this ability ignores freedom of movement effects.
Stygian scales:Ex At 11th level the Styx dragon gains DR/magic and good equal to half its total HD and SR equal to its total HD plus 11
Stygian influence: After swimming through the river Styx for centuries the planes they swim through have affected the dragon's attacks. At 12th level The Dragon can now bypass any form of damage reduction that can be bypassed by any evil alignment as if their weapons were attuned to that alignment.
Stygian Corruption: No mind can resist the river Styx. The Stygian dragon can now affect creatures immune to mind affecting with his Mind Affecting SLAs, but those creatures receive a +4 bonus on their saves.
Crush: At 12th level the dragon can make a crush attack dealing 2d8 damage base, already taking in acount huge size
This special attack allows a flying or jumping dragon of at least Huge size to land on opponents as a standard action, using its whole body to crush them. Crush attacks are effective only against opponents three or more size categories smaller than the dragon (though it can attempt normal overrun or grapple attacks against larger opponents).
A crush attack affects as many creatures as can fit under the dragon’s body. Creatures in the affected area must succeed on a Reflex save (DC equal to that of the dragon’s breath weapon) or be pinned, automatically taking bludgeoning damage during the next round unless the dragon moves off them. If the dragon chooses to maintain the pin, treat it as a normal grapple attack. Pinned opponents take damage from the crush each round if they don’t escape.
A crush attack deals the indicated damage plus 1½ times the dragon’s Strength bonus (round down).
at 12th level the dragon gains frightful presence. ability takes effect automatically whenever the dragon attacks or charges. Enemies within a radius of 30 feet × half the dragon's level are subject to the effect if they have fewer HD than the dragon. A potentially affected enemy that succeeds on a Will save (DC 10 + ½ dragon’s HD + dragon’s Charisma modifier) remains immune to that dragon’s frightful presence for 24 hours. On a failure, enemies with 4 or less HD become panicked for 4d6 rounds and those with 5 or more HD become shaken for 4d6 rounds. Dragons ignore the frightful presence of other dragons.
Bonus feat: At levels 13, 15 and 20 the Styx Dragon gains Extrarodinary disease as a bonus feat (see after this monster entry) or a fighter bonus feat for wich it qualifies for.
Stupefying breath:Su At 14th level the dragon gains an additional breath weapon. The breath is a cone with a radius of 30 feet+5 feet per HD of the dragon and deals 1 intelligence damage for every 3 HD of the dragon. The damage can be halved with an appropriate fortitude save of DC 10+Con Mod+Half its HD. The breath weapon recharges in 1d4 rounds.
Disease ascension: At 15th level, the dragon can now bypass immunity to disease derived from class features (Such as the Paladin's divine health) and any ability not derived from a creature's type. However, Styx dragons cannot affect each other with this ability. In addition, the damage die for both Stygian wasting and devil chills increase by one die size.
Corrosion: At 16th level, the Stygian Dragon's natural weapons deal an aditional 1d8 Acid Damage. This Damage increases one die step for every 4 HD gained from here.
Stygian bite: At level 17 the Styx Dragon's bite is a weapon to be feared. The Dragon can now channel its Stupefying breath weapon into its bite attack to be used along with it. This still counts as a use of the breath weapon and you must wait 1d4 rounds before using the breath weapon in any way shape or form again. Channeling the breath weapon is a swift action.
Disease Body: At 18th level all of the Styx Dragon's natural weapons can transmit diseases as his tail.
Tail sweep:At 19th level this special attack allows a dragon of at least Gargantuan size to sweep with its tail as a standard action. The sweep affects a half-circle with a radius of 30 feet (or 40 feet for a Colossal dragon), extending from an intersection on the edge of the dragon’s space in any direction. Creatures within the swept area are affected if they are four or more size categories smaller than the dragon. A tail sweep automatically deals 2d6 plus 1½ times the dragon’s Strength bonus (round down). Affected creatures can attempt Reflex saves to take half damage (DC equal to that of the dragon’s breath weapon).
Pestilence:At 19th level the Styx Dragon can contaminate anything it touches. As a fullround action the Styx dragon can "rub" the area where he's standing or a number of objects equal to his Con modifier. The next creature steping on that area or touching the object willingly receives a disease as if hit by the Styx's dragon natural weapons, same Fort Save to resist. The disease must be chosen when the Styx Dragon rubs. The effect is permanent but each contaminated square /object can only try to infect one creature per HD. A rogue can spot and safely "clean" an object with his trap sense, search and disable DCs are 10+HD+Con modifier.
Disease perfection Su: At 20th level, the Styx dragon's affinity for disease has reached it's peak. From this point on, the dragon's disease based abilities* affect even those normally immune to them. The dragon now bypasses any immunity derived from type, race, class, or anything else besides being a Styx dragon (or summoned by a Styx Dragon). Styx dragons are still immune to each other's diseases. In addition, anything that is not normally immune to disease receives no save and the saves on the disease are now equal to the save of the dragon's breath weapon.
*The abilities that disease ascension and perfection apply to are the dragon's tail blades, its SLAs, and any spells it can cast due to the class.
Comments
The Styx Dragon can't fly, but it swims and burrows quite well. It has a powerfull array of SLAs and disease abilities to back up it's melee-grappling abilities and bard-sorceror spellcasting.
If you feel like playing an aquatic dragon that lays down plagues upon his oponents, the Styx Dragon's for you!
In addition to the features described herein, there are new feats to enhance the Styx dragon's disease based abilities. (Credit to Hyudra)
Extraordinary Disease [Monstrous]Your disease works in a manner above and beyond that of other creatures of your type.
Prerequisite: A natural weapon that can transmit disease, 13 Con and 6HD, at least one of which must be a level in a monster class.
Benefit: Choose one of the following from the list to enhance your diseases:
- Pathogen: Each time the victim fails a save against the disease (including the initial save to find if the disease was contracted), the DC is increased by +2.
- Rapid Onset: The Disease now has an incubation period of 1d3 rounds. This may be taken a second time, reducing the incubation period to 1d3-2 rounds.
- Scourge: The victim must save against the disease twice as often (ie. from every 24 hours to every 12 hours). This option may be taken multiple times, halving the amount of time the victim must save each time it is taken. (from 24 to 12, 12 to 6, 6 to 3, and so on).
- Fever: Once the poison enters the victim's system, the victim displays a rapidly progressing fever. From the point the victim fails the saving throw up until the time the disease is removed, the victim is Fatigued. Once the disease is incubated, the victim must make a fortitude save on any given hour or Exhausted, instead. (DC is 10 + ½ creature's HD + creature's Con)
- Systemic Shock: When an opponent fails their save against disease, they are immediately sickened. Further, if the disease affects physical stats, the creature must make another fortitude save or be nauseated for 1d4 rounds, and if the disease affects mental stats, the creature must make a will save or be confused for 2d3 rounds. The DC for both saves isis 10 + ½ creature's HD + creature's Con.
Once the disease has incubated, the victim must save or be nauseated/confused (again, as appropriate to the disease) on any given hour.
- Miasma: After a disease has finished incubating, a contagious vapor begins leaking out of their nose and mouth to taint the air around them. The disease effectively becomes inhalation and contact based, transmitted with the victim themselves as the origin point. Any infections transmitted in this way have the traits of the original disease, but with only a 50% chance the new victim will also show signs of the miasma.
1d3 rounds after a victim afflicted with Miasma dies, the miasma begins consuming their body, filling all adjacent squares with the inhaled version of the disease.
- Blight: The disease becomes potent enough to affect targets that are normally immune, as the individual elements in the disease produce byproducts that consume, occlude or taint even inanimate matter or energies. The Disease can now affect any creature that cannot produce the disease itself, including those creatures that are typically immune or that lack constitution scores. The effects of the poison are halved when affecting such opponents, rounding down. Diseases that would deal Con damage to creatures with no Con score deal Cha damage instead.
This feat may be taken multiple times, choosing a different option each time (or choosing options that specifically allow multiple instances).
Contributed by Kyuubi from GITP
