Don't forget: AC bonuses generally don't add to CMD. Even with +6 dex on a +10 AC light armor (which I'm not even sure how that's possible without it being an artifact) you still only have at best a 10+4 Str + 6 dex + 3bab = 23 CMD. What can you do with that?
Greatclubs, earth breakers, and any other weapon in the hands of a large creature (undead troll?) or enlarged creature can sunder armor, weapons with reach. Untrained the attack provokes an an attack of opportunity, but with reach the PC can't take it. Hide has low hardness and not great hit points- even if it only gets to "broken", the item loses half it's AC bonus. Plus, if you destroy the weapon the character is wielding, it doesn't matter how much AC he has.
The BBEG may even have a Skeleton Champion with fighter levels who specializes in this (power attack, improved sunder, greater sunder).
Take away the fighter's weapon.
A herd of rampaging, charging, undead bull rushing cattle rushing the characters towards some dangerous obstacle (pit, ooze, spikes, etc). Knock them around. Keep them where your BBEG wants them: away from him. Have. Few ready actions to bull rush when the player (any of them) moves in to attack. Any animals with lots of strength and little else make great zombie bull rush servants. (Horses, or Aurochs if you feel they can handle it).
Spell component pouches are so pesky. That new familiar your BBEG gets could have improved steal...and try to grab the little bag your caster carries that enables all it's spells. A perception check vs an invisible tiny creature' sstealth check while distracted (what player won't pay attention to the BBEG's monologue ... -4 penalty on that check)
Again, reach weapons and untrained enemies or trained enemies with any weapon can make things a nightmare for full attackers. Ready to do it right as the player goes to attack. The maneuver goes off before the player action, so if prone, the player has the prone penalty on any attack. Remember that standing up provokes an AOO too...which could be a disarm or sunder attempt.
In addition to pinning, you can deal damage, or move half your move speed.
In fact, readying combat maneuvers for players to act to thwart their actions is generally really valuable against many kinds of targets. Examples:
- Ready a move action to approach ranged characters, so they provoke AOO's when they attack. Disarm or trip with the AOO.
- Ready an attack vs spellcasters so they have to make a concentration check vs damage OR resisting a spell.
- Ready a move for minions to intercept players advancing on the BBEG. If they fight the minion, sweet. If they continue their move, AOO. You can sunder, disarm, of trip on an AOO. (See above) The Combat Patrol feat gives you this ability, AND an automatic attack...great for bodyguard types.
Spellcasters use spells. Fighters use hitpoints. Armor takes damage. Consumables get used. Throw one or two specialized tricks at them regularly to keep them guessing, keep them on their toes. Make them think they've reached the end before they actually do...then do it again. Strain their ability to hold back on their limited abilities.
If your world is full of artifacts that grant your players great power, who says the enemy doesn't have the same? The BBEG may very well have a fighter of nearly equal skill that if anyone but your Drow player fought, would die nearly instantly. Barbarian monstrous humanoids with die hard, toughness, tribal scars, buckets of Con, a cheap potion of barkskin, a casting of bear's endurance, and a mysterious alchemical infusion (Monstrous Physique can turn a normal enemy into an armored, hitpoint hulk. Check out the 4 armed gargoyle. Gross.) Throw a single mythic template on him to increase the hitpoints yet again...and give all new, super scary abilities. (The Dual Initiative mythic monster ability for one can turn a normal semi-scary hulk into a Very Big Problem.)
Swarms don't make attack rolls. They auto hit, and usually take no damage from weapon attacks. They are the bane of most weapon fighters.
Ghosts, Shadows, Allips, Spectres, all deliver their attacks with incorporeal limbs, bypassing armor bonuses.
Lots of touch weapons exist: alchemist fire, acid, etc. Brilliant Energy weapons are expensive, but as GM, you could supply an NPC a few brilliant energy arrows.
The little guys. The waves of skeletons that doesn't seem to end. They go down in a swing...but there's so many. The powerful character will have to decide between defending his party or leaving them to the swarm he can easily handle.
The BBEG has probably prepared his final lair to defend himself. Your players won't get a chance to look for all the traps he has laid about. Pits, falling things, exploding things, rubble, barriers, hazards (fire/freezing water/necrotic goo) all can slow a party down/ make them work on their tactics.
Your BBEG will almost certainly NOT start next to your players. Make them come to him, on his terms.
Other BBEG allies
Great additional minions:
- Witch with Evil Eye and Cackle hex. Every turn, auto penalize attacks, AC, or saves to the BBEG's biggest threat, and keep them up until the fight is over. With Greater Invisibility on her, she becomes a nearly unstoppable debuff machine.
- Bard (level 1) - intelligent undead can benefit from inspire competence.
Each of those BBEG allies could be intelligent undead themselves.
Oh, spells. Let me count the ways.
Touch Attack Spells
A ton of spells are touch attacks or AoE attacks. Scorching Ray, ray of enfeeblement, etc. Gloomblind Bolts are a rare spell that can even bypass most energy resistances.
Desecrate the BBEG's final lair. Make sure it has an altar to an evil deity in it. Your undead gain massive bonuses as a result, and your BBEG can create more undead than normal.
clouds / mists
Fog Cloud is a classic way of hiding from enemies. Searching must be done square by square...ish. Hidden doors and secret passages coupled with fog make for good misdirection.
Don't split the party is the #1 rule. These spells make it reality. Combine this with the "champion" suggestion and you force that grand confrontation between your high powered PC and the scary NPC opponent.
Web / Black Tentacles / Solid Fog
Difficult terrain. grappled condition. Reflex save. Burns people alive stuck in it.
Evasion spells (Blink, Blur, Mirror Image)
Up to eight miss chances. Can be coupled with Blink or Blur for additional concealment/miss chances.
Make one or more characters your BBEG's pet...of at least, take him out of the act for a moment. Something reasonable with a suggestion ("Flee...it's your only chance!") can last for hours a level. Can even use them as a hostage against the others.
Mooks, once killed, return to fight again with a touch. Glorious day. With a reach metamagic rod, BBEG can even do this at a distance.
Darkness / Deeper Darkness / See in Darkness / Tremorsense / Lifesense / Invisibility / Greater Invisibility
What you can't see, you miss (50% of the time). What you can't see, you can't target (spells). Any BBEG who uses this tactic probably has an alternate way of seeing-see in darkness (popular among undead types), darkvision (if the room doesn't go supernaturally dark), or another sense (Echolocation is a great spell for that...even if it has to come from a scroll.)
Summom Monster/Nature's Ally
More threats, SLA's, and attacks. A lion can charge, pounce, and get rake attacks all in one go once it appears. For Undead BBEG, he can take "Skeletal Summomer" and bring forth skeletal campions of skeletal versions of anything once per day. An undead Monkey Swarm (see swarms, above, an the Mad Monkeys spell) would be hilarious and incredibly powerful at counter balancing your fighter.
Rays / touch spells (Ray of Exhaustion, feeblemind, bestow curse)
Stat reducing spells or curses can slow down enemies quite nicely.
A side note on APL with Drow Noble
According to Jason Buhlman, a Drow Noble should be treated as a CR +1. Coupled with that armor, you might really have an effective level 5-ish character. You will want to adjust the APL for you party accordingly. ( http://paizo.com/forums/dmtz1oeq?Bestiary-Drow-vs-Noble-Drow#11 )
Even after that adjustment, For a boss fight, you can have your CR 3 or even 4 above their APL. They should barely make it out...if at all. A player may die. If you make the fight challenging enough, and make sure everyone contributes, then it will be a glorious death, one to remember. In the end, it's about remembering the story.