Do you mean you want your half dragon dire boar to have class levels? Barbarian would be the obvious pick.
You may be referring to something that used to exist in 3.x. In Pathfinder, that's just adding racial hit die.
http://paizo.com/pathfinderRPG/prd/bestiary/monsterAdvancement.html#adding- racial-hit-dice
If you scroll down a little you can also see the option to add class levels instead. In this case, I think you'd get a lot more for less work by just adding some levels of barbarian.
I second the motion for barbarian. Go all erimanthic boar there :)
With 6 levels it would get enhanced movement, improved uncanny dodge, rage and three rage powers.
Fearless rage, rolling dodge, surprise accuracy, terrifying howl or internal fortitude might be fitting rage powers. Rage powers give small bonuses, so don't expect too much from them.
From the base data it would have:
AC 15 (changes to 19)
HP 42 (5d8+20) changed to 138 (5d8+6d12+77)
Saves: +7,+4,+2 changed to +15,+6,+4
Speed: 40 changed to 50
Melee: gore +8 (2d6+9) changed to +18/+13 (2d6+13)
When raging (for 20 rounds) he gets +4 STR and CON and -2 to AC and +2 to will saves. That leaves us with 160 hp and another +2/+2 in melee.
From the barbarian levels it would also gain 3 feats. Power attack, weapon focus and improved critical could fill that for a raging boar. Power attack, furious focus and step up are also nice.
For your convenience, the rules from the PRD:
Creating a Half-Dragon
"Half-dragon" is an inherited or acquired template that can be added to any living, corporeal creature (referred to hereafter as the base creature). A half-dragon retains all the base creature's statistics and special abilities except as noted here.CR: Same as the base creature + 2 (minimum 3).
Type: Creature type changes to dragon. Do not recalculate HD, BAB, or saves.
Armor Class: Nat. armor improves by +4.
Special Qualities and Defenses: A half-dragon gains darkvision 60 feet; low-light vision; and immunity to sleep, paralysis, and energy of the same type as its breath weapon.
Speed: A half-dragon has wings. Unless the base creature has a better fly speed, the half-dragon can fly at twice the creature's base land speed (average maneuverability).
Melee: A half-dragon has two claw attacks and a bite attack. If the base creature can use manufactured weapons, the half-dragon can as well. A new claw or bite attack deals damage as appropriate for the half-dragon's size (see Natural Attacks.)
Special Abilities: A half-dragon retains all the special attacks of the base creature and gains a breath weapon usable once per day based on the dragon variety (see below). The breath weapon deals 1d6 hit points of damage per racial HD possessed by the half-dragon (Reflex half; DC 10 + 1/2 creature's racial HD + creature's Con modifier).
Dragon Variety Breath Weapon
Black or copper 60–foot line of acid
Brass 60–foot line of fire
Blue or bronze 60–foot line of electricity
Gold or red 30–foot cone of fire
Green 30–foot cone of acid
Silver or white 30–foot cone of cold
Abilities: Increase from the base creature as follows: Str +8, Con +6, Int +2, Cha +2.Skills: A half-dragon with racial Hit Dice has skill points per racial Hit Die equal to 6 + its Intelligence modifier. Racial class skills are unchanged from the base creature's.[/quote
The intelligence does increase. Its type changes to dragon, so there shouldn't be any doubt.
What level is the party that will be facing this?
Hear is a set of stats based on racial advancement (and Monster Creation Balance) instead of class advancement.
Based on what you've given so far, I'd estimate your creature to be around a CR 9 according to the Monster Creation section. I might conclude differently when I finish statting it out.
If you want to advance it 6 levels as an animal, then the easiest way to go about it is to do just that to a normal Dire Boar, and then add the Half-Dragon template. The result:
N Large animal
Init +4; Senses darkvision 60 ft, low-light vision, scent; Perception +18
DEFENSE
-------------------
AC: 23 (+14 Nat, -1 Size)
HP: 11d8+77 (126 hp)
Fort +13 Ref +7 Will +6
Defensive Abilities: Ferocity, Immunity to (Energy), Immunity to Paralysis, Immunity to Sleep
OFFENSE
-------------------
Speed 40 ft, Fly 80 ft (Average)
Melee: Gore +19 (2d6+11), Bite +14 (1d8+5), 2 Claws +14 (1d6+5)
Special Attacks: Breath Weapon (1/day, 11d6, DC 21)
STATISTICS
------------------
Str 32, Dex 10, Con 23, Int 4, Wis 13, Cha 10
Base Atk: +8, CMB: +20, CMD: 30
Feats: Improved Initiative, Skill Focus (Perception), Toughness + 3 new ones (Recommending Power Attack, Iron Will, and Improved Iron Will as included in the stats)
Skills: Acrobatics +11, Fly +9, Perception +18
Completion Notes: It's actually about average for a creature of this challenge rating. The average damage is a little high, as is the HP, but both the Reflex and Will saves are a little low. Thus, I'd probably continue to call it a CR 9 monster.
EDIT Okay, never mind. Just don't forget that Constitution and Charisma are both also increased, and that advancing this thing by 6 levels means that it has 1 point ability increase coming to it as well.
Hi Malligant, thought I'd chime in and help.
First of all, high BAB bonus won't give creatures with natural attacks extra attacks (see the poor t-rex as an example)
You have the HD for this creature all on one line so I'm not sure of the mix but here's my guess at its attack.
1) 5HD animal will be a +3
2) 6 levels of barbarian for another +6 for a total of a BAB of +9
3) this is for combat, we can usually assume raging for a Str of 36 (+13)
So I believe all of its attacks will be at a +22 as gore, bite and claws are all listed as primary attacks in the bestiary. It is common though for claws to be secondary attacks, in which case they would be at +17.
This thing would wreck most level 6 parties. A Half-Dragon Dire Boar is already CR 6. Adding 6 barbarian levels makes it CR 12. Of course, if the party is extra large or full of min-maxers, that may be a doable boss fight. Otherwise, you may want to drop the Barbarian levels to 3rd or 4th.
I agree. This would easily go through most 6th level parties.
I included the 2nd attack due to the 6 barbarian levels, but maybe I went overboard with that. Still, there are no secondary listed for the boar, and two attacks seemed not overwhelming for a "boss".
It does get wings and a breath weapon, but the damage is 5d6 (it has only 5 racial HD), so it is not that powerful. If it is based on a red dragon, the cone of fire should get 2 or 3 of the party as an opening and will put them on their toes, even if it never uses it again.
The CR rating on such monsters is somewhat misleading imo. It has only one action against all of the party, which puts it at a disadvantage. The thing making it dangerous are his immense HP, which ensure it will be around for a few rounds, and the ability to fly+breath if no one can counter that.
A half dragon gets two claws and a bite. So, this creature should have 4 natural attacks, including its gore. Though some may argue that the gore and bite can't be used at the same time, since they use the same "appendage".