Two cohorts for a BBEG

[Eonir]

So BBEG is a Vampire Lord Dread Necromancer. As a 20HD vampire he can have up to 40 HD of vampires under his control. I decided he'll have two 20HD.

I am thinking they should be a Dark Companion Hexblade and a DFI Bard (there will also be plenty of undead minions to be annoying). What does the playground think?

[Waker]

That's kind of vague. What levels are the party likely to be when they face the vampires? What is the make up of the party and their usual tactics? Did you have a particular goal in mind when making the vampires?

[Doxkid]

What exactly are you looking for each cohort to be like?

Do you have a roles for the cohorts in mind?- That'll really help us help you.

How powerful do you want this trio to be?- I could just say 2 more level 20 Dread necromancers, or the Word/Wish duo or...

What kind of setting is the game in?- High magic, low magic or in between?

Where is the BBEG?- Making one cohort capable of controlling his domain gives you a lot of options just for the party trying to reach the trio.

Who works with the BBEG?- Does he have the backing of a Gnoll queen? Is he buddy buddy with a few mindflayers (relatively speaking, since they mostly hate everyone and everything)?

What is the BBEG's goal?- World Domination? Carving out a nation for himself? Laying the world to rest? Preserving the world's beauty?

What does the BBEG think of Group X and Group Y and Group Purple and the PC's team?- Are paladins hunting him (Futilely, or not)? Are Celestials popping into this world trying to track him down and make him pay for his crimes?

What has the BBEG been doing so far?-Sending wave after wave of undead at the party? Assaulting a keep? Building a keep? Trolling churches?

Who else is working to stop the BBEG?-The two cohorts might have been selected specifically to deal with two of the BBEG's largest threats.

What is the BBEG's build? And favorite spells? What Advance learning spells did he select? Does he only cast, or does he also melee?-This is pretty major. Also, depending on your answer, he could pick up two levels of Master Vampire, forgoing the last 2 levels of Dread necromancer in exchange for more/better minions.

He loses:

Craft Wondrous-a feat he doesn't need since he wont become a lich anyway.
One 9th level spell slots per day
His last Advanced learning spell-this is the only major loss.
Some uses of his enervating Dread Necromancer touch
Two levels of Familiar progression

and gains:
Turn resistance that increases by 1 for every spawn within 60 feet.
He adds his charisma modifier to his hit die when determining the maximum number of spawn he can control.
His spawn gain a +2 enhancement to strength and dexterity
4 extra skill points.

Just taking 1 level of Master Vampire gets him boosted spellcasting, +2 to his fort and will saves, the maximum spawn boost, and the turn resistance in exchange for absolutely nothing.
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With no additional information coming from you, I'll simply suggest making one cohort capable of expanding your minion list so Undead/vampire/vampire thralls isn't all that team has going for it.

Stunt spell progression so neither reaches 8th level spells, making the party actually killing these guys reasonable but still difficult. This gives you a lot of room to pick up flavorful abilities that will up the challenge, but make holding back unnecessary.

What minions are you currently using? It would be easy and logical for one of those cohorts to be the highest progression of a certain type of opponent the party faces often.

Alternately, one of the cohorts could be a minion-mancer in and of himself. Having a corrupted Malconvoker in this trio will let you warp things decent pets.

How do you feel about Fleshwarper? One of the cohorts being a mad scientist that does things like add artillery to giants might work for you.

[Zilzmaer]

Vampire Lord, unlike Vampire, has no HD limit for spawned vampires. Also, keep in mind that many bardic musics won't work on undead, so you'll have to look into Requiem or the like.

[Doxkid]

Vampire Lord, unlike Vampire, has no HD limit for spawned vampires. Also, keep in mind that many bardic musics won't work on undead, so you'll have to look into Requiem or the like.

Ah, right. The 'Never break free" part coming into play.