OK, when I statted him out, I just used the book stats. Let's play with the Elite Array from
the book and see what we can do to his stats. We will make the "dump stat" Strength since it
will be "hidden" by all the bonuses.
Elite Array changes, in order: -2, +4, +2, +2, +0, +4
Better AC, better HP, better skills, better save DC's for Ogre Mage abilties.
For his 4th level Stat increase, we will bump up Dex.
Recomputing skills based on Improved Intelligence
He should get 2 feats for character levels
EDIT: Oh, I just noticed that Spell Resistance is suggested to be 11+CR for creature. If we go with the hypothetical CR of 11 before class levels, that will bump SR to 22
Class skills:
Ogre Mage: Concentration, List, Spellcraft, Spot
Snake: Balance, Climb, Hide, Listen, Spot, Swim
Rogue: Appraise (Int), Balance (Dex), Bluff (Cha), Climb (Str), Craft (Int),
Decipher Script (Int), Diplomacy (Cha), Disable Device (Int), Disguise (Cha),
Escape Artist (Dex), Forgery (Int), Gather Information (Cha), Hide (Dex),
Intimidate (Cha), Jump (Str), Knowledge (local) (Int), Listen (Wis),
Move Silently (Dex), Open Lock (Dex), Perform (Cha), Profession (Wis),
Search (Int), Sense Motive (Wis), Sleight of Hand (Dex), Spot (Wis), Swim (Str), Tumble (Dex), Use Magic Device (Cha), and Use Rope (Dex).
Sorceror: Bluff (Cha), Concentration (Con), Craft (Int), Knowledge (arcana) (Int), Profession (Wis), and Spellcraft (Int).
It looks like we have a lot of overlap. We probably want to take a bit of Disguise so you can pull off the polymorph gambit convincingly.
Feats: We will take the Two Weapon fighting chain. Add in Improved Initiative and a long sword proficiency and we still have 3 feats left
Spells: I've dropped in Mage Armor since it has good mileage and is an easy one for him to apply before the PC's meet him in combat. Besides, it is a force affect and protects nicely.
Familiar: He is a Sorceror. The only book familiar that makes a lot of sense is a viper. This will give him a +3 on Bluff checks. Alas, the Viper won't have much in the way of HP.
So, what do we have so far?
----------
Bothriechis Din Woad, Male Half Ogre Mage/Half Giant Constrictor Sor 2 Rog 2: CR 15?;
Huge Monstrous Humanoid; HD 16d8+32 (creature) plus 2d4+4 (Sor) plus 2d6+4 (Rog);
HP 124;
Init +10;
Spd 20 ft, climb 20 ft, swim, 20 ft, fly 40 ft (good);
AC 23 (-2 size, +5 Natural, +6 Dex, +4 Mage Armor) touch 18, flat-footed 17;
Base Atk +18; Grap +32;
Atk +24 melee (dam/crit, weapon);
Full Atk +24/+19/+14/+9 melee - single weapon, +22/+17/+12/+7 long sword +22/+17/+12 short sword
SA spells, sneak attack, Constrict 1d8+9, Improved Grab, Spell-like abilities (See Ogre Mage);
SQ Darkvision 90ft, Evasion, Low-light vision, regeneration 5, spell resistance 22, trap finding;
SV Fort +11, Ref +18, Will +10;
AL NE;
Str 23, Dex 22, Con 15, Int 16, Wis 14, Cha 21.
Skills: 95 (Creature - 2+3 * hd+3)+22(Rog)+10(Sor)= 127
Feats: 6 (for Creature HD) +1 (1st level) +1 (3rd level) = 8
Martial Weapon Proficiency: Long Sword, Two Weapon Fighting, Improved Two Weapon Fighting, Improved Initiative,
Greater Two Weapon Fighting, + 3 more
Languages: Common, Draconic, Giant, and Infernal.
Spells per day: 0 level 6/ 1st level 5
Spells Known(5/2; base DC = 15 + spell level):0-[cantrip,cantrip,cantrip,cantrip,cantrip]; 1st - [Mage Armor, first].
Spell-Like Abilities: At will - darkness, invisibility; 1/day - charm person (DC 16), cone of cold (DC 20), gaseous form, polymorph, sleep (DC 16).
Flight: Resume flight as a free action. While in gaseous form can fly at normal speed and has perfect maneuverability.
Regeneration: Fire and acid deal normal damage.
Constrict: On a successful grapple check, deals 1d8+9 damage.
Improved Grab: To use this ability, Bothriechis must hit with both sword attacks. He can then attempt to start a grapple without provoking an attack of opportunity. If he wins the grapple check, he establishes a hold and can begin to constrict.
Possessions: ??
Tactics: ??
Bothriechis prefers to operate with subterfuge in most cases. However, he does prefer to mete out punishment personally.
When encountered in his lair, he will use his spell-like abilities to harass the PC's, finally using his innate powers of invisibility to flank a PC when they are fighting his underlings. When he finally engages in melee, it will be from a flanking sneak attack position. The potential for 7 melee attacks with +1d6 sneak attack on each one should provide some wonderful looks of surprise on your players' face.
Pogre: OK, a huge snake with a blue ogre's torso appears next to your cleric. He is flanking off of mook #3. Let's see, he swings (pogre rolls a d20, then keep rerolling six more times.) What do you know, he hit every time. OK, let's see how much damage that is. (pogre picks up 4d8 and 10d6, shakes in hands liberally, tosses the dice onto the table and asks the players to count up the damage) OK, now add 42 for bonuses. How many HP did your cleric have? (BTW-Average damage with that will be 95.)
Then the PC's will likely turn their attention to Bothriechis. Imagine their dismay as regeneration kicks in. Yeow.