In charge of making a Boss Fight, need help balancing things!

[Darksol the Painbringer]

As the title.

Basically, I designed a BBEG for the GM to throw at us, and he's decided to put me in charge of running the encounter (he'll play my PC, which will be interesting). There is a party of 5 PCs, and they will be fresh at 8th level when they face the encounter. The party composition (with basic descriptions) is as follows:

1. Vanara Druid (Mehnir Savant, Fire Domain), strong in casting, functional in melee
2. Elf Magus (Strength Based), extreme burst damage
3. Ratfolk Alchemist (Plaguebringer), strong bombs and crowd control via Smoke Bombs
4. Human Monk (Vow of Poverty, can't equip any items), Dexterity-based, Crane Style melee type
5. Fetchling Ninja (Standard class type), Dexterity-based, TWF with Wakizashis.

Here's some relevant houserules:

Houserules:

1. Charisma is gone. It's not an attribute. Its types have been replaced with other attributes, as appropriate (such as Strength for Intimidate, Intelligence for Bard Spellcasting, Wisdom for Paladin abilities, and so on).

2. Weapon Focus, Shield Focus, and their Greater variants are gone as well. They are not feats, nor are they considered pre-requisites for feats that call for them. (Specialization feats are still present.)

3. Power Attack and Point-Blank Shot are free feats given to all characters if they meet the pre-requisites. All other feats must still be taken as normal.

4. PCs were given up to 15 RP to work with their chosen race (that is, the PCs could choose up to 15 - their chosen race's RP value in additional Racial Traits).

5. Automatic Bonus Progression is enabled. Creatures use their hit dice + 1 to determine ABP benefits.

The Scenario:

Effectively, the PCs are investigating a ruined temple for a portal back home. When they come into the boss room, they'll spot the BBEG (well, the BBEG will probably spot them before they spot her). She will go on a tirade about having all of these interruptions for her quest to reclaim that which was taken from her (a long story, basically two dragons decided to kidnap her children and killed the war hero husband that was trying to defend them in a single swipe of their claws, because within her, as well as her progeny, flowed the dormant blood of dragonkind; she realized that she couldn't physically do something about it, but she wished she had it, the power to protect her offspring. The only thing she knew was that she had to fight fire with fire, in a sense, and went on a quest to access the strength of dragons). She will then praise their power and tenacity, and say that in truth, she isn't currently prepared for them, and that she'll have to use what she came here for well before the time that she wanted to use it; clenching the Dragonsblood Elixir in her hand, she drinks it, unleashing her hidden power to take out on the PCs (and eventually the dragons that stole her children).

Now, I originally planned the boss to be 9th level (2 levels above the PCs), having 5 levels of Bloodrager with the Draconic Bloodline, and 4 levels of Dragon Disciple (as I expected us to be 7th level fighting her), granting her SR = 11 + HD, and +2 Natural Armor. She'll also have maximum HP for the HD, since she's the boss and all.

But, with the PCs being 8th level, I could bump her up to 10th level (taking another Bloodrager level), tack on the Half-Dragon template (and ditch the +2 Natural Armor for something else), or do both, and fit the story's flavor a lot better (showing that the elixir brings out the Dragon Disciple levels and bringing her to Half-Dragon status). The downside to doing that though, is that I fear I'll be making her too strong for the PCs to deal with.

There's also the matter of throwing in minions; if I buff her up to the desired level, would throwing in minions be overkill, or would I still have to, just to keep the BBEG from getting slaughtered by action economy? And if I do throw in minions, what kind of minions would be appropriate for her (preferably something that would mesh quite well with her build and concept)?

For what it's worth, here's the current build of her, here.

Bumping her up a Bloodrager level would provide an extra BAB, Toughness (bloodline feat), plus an extra 1st level spell. The Breath Weapon will deal 10D6, with a Save DC of 20. It will put her base HP at 158, with her raging HP at ~188. A sizable increase, but really only in the HP department.

Adding the Half-Dragon Template would provide an extra +4 to-hit and damage (or +6 with 1.5x Strength attacks), ~2 AC, an extra 30 HP (and +3 to the Breath Weapon Save DC), and other goodies.

So, what should I do?

[Bandw2]

what I do when I want a boss to be deadly and not need minions, I give them X4 HP and 4 initiative rolls (none of them can be sequential, they need a player turn in between each of them) every 1/4th of the HP knocks off the next initiative roll. Debuffs only effect the next initiative if they limit action economy.

do that and you should be fine probably.

I call it the boss template CR +2.