Wow, what a fun dilemma!
First off, let's aid the villain. A contingency teleport would be nice (Set to teleport him to some safe location if he is reduced to 10 or fewer hit points, is incapacitated/paralyzed, or loses control of his mental faculties. Give him some buffs, potions, invisibility, poisoned weapons... if possible give him vision in darkness, and a gust of wind to take out any torches and lanterns, a quick dispel by his friendly mage could wipe out magical light, followed by the cleric's silence spell. How well will the PCs fight if they can't see? Does your wizard dare drop a fireball, not knowing where his allies are? Can the wizard even cast it in the magical silence?
Second, how about a pet advanced rust monster that has improved invisibility for the opening combat? Take out a few of those helpful defenses. Also, he should have a cleric or sorcerer to help him out with healings and stoneskins and displacement-type magics. Also to Bane/Slow/Wall of Force as needed. Add their golems and conjured demons.Also, an army of useless creatures to take actions away from the main opponent/villain. If you put it a couple hundred goblins that worship the villain, they can grapple and thrown acid, and otherwise be a nuisance that requires attacks to disperse.
Third; terrain is your friend. If the PCs are attacking, they have to go through layers of traps (magical and mundane), servants, secret doors (can't kill him if you can't find him!), physical impediments ("We need to get that block out of the way before we can continue down to the next level of the temple, guys."), and puzzles (Sure, you can outfight the villain, but can you outsmart him?). Put a time-limit on them in some way. Perhaps the villain has a huge spell prepared that will destroy the city if not stopped before midnight. Use the terrain to batter the PCs a bit. Get them to use divination, healing, buffs, potions... Tenderize them before the big fight. Not only will this make the fight more challenging, but it will become a legend when they retell the story of their characters overcoming incredible odds to save the city.
Fourth, let's focus on some role-playing. Can the monk attack the villain, if said villain has his mentor/friend/sister at knife point? What if he holds a detonating device that would, if the villain isn't concentrating (ie. he's dead) will explode, collapsing the stone temple everyone is in, killing them (or creating a possibility of an adventure to find their way out from the tons of rock now atop them)?
In short, don't fight fair. Make 'em sweat, don't be breaking the rules, but use the rules and story to make the battle absolutely epic! Use a lot of descriptions of rooms (you'll be surprised how many spells and resources PCs will use to check out mundane stuff if you describe them well enough), create atmosphere (spider-webs and shed snake skins, corpses long dead (and fresh!), darkness, shadows, sounds echoing, smells of decay, trip-alarms... go to town.
This could be the battle of the players' lives!
First off, let's aid the villain. A contingency teleport would be nice (Set to teleport him to some safe location if he is reduced to 10 or fewer hit points, is incapacitated/paralyzed, or loses control of his mental faculties. Give him some buffs, potions, invisibility, poisoned weapons... if possible give him vision in darkness, and a gust of wind to take out any torches and lanterns, a quick dispel by his friendly mage could wipe out magical light, followed by the cleric's silence spell. How well will the PCs fight if they can't see? Does your wizard dare drop a fireball, not knowing where his allies are? Can the wizard even cast it in the magical silence?
Second, how about a pet advanced rust monster that has improved invisibility for the opening combat? Take out a few of those helpful defenses. Also, he should have a cleric or sorcerer to help him out with healings and stoneskins and displacement-type magics. Also to Bane/Slow/Wall of Force as needed. Add their golems and conjured demons.Also, an army of useless creatures to take actions away from the main opponent/villain. If you put it a couple hundred goblins that worship the villain, they can grapple and thrown acid, and otherwise be a nuisance that requires attacks to disperse.
Third; terrain is your friend. If the PCs are attacking, they have to go through layers of traps (magical and mundane), servants, secret doors (can't kill him if you can't find him!), physical impediments ("We need to get that block out of the way before we can continue down to the next level of the temple, guys."), and puzzles (Sure, you can outfight the villain, but can you outsmart him?). Put a time-limit on them in some way. Perhaps the villain has a huge spell prepared that will destroy the city if not stopped before midnight. Use the terrain to batter the PCs a bit. Get them to use divination, healing, buffs, potions... Tenderize them before the big fight. Not only will this make the fight more challenging, but it will become a legend when they retell the story of their characters overcoming incredible odds to save the city.
Fourth, let's focus on some role-playing. Can the monk attack the villain, if said villain has his mentor/friend/sister at knife point? What if he holds a detonating device that would, if the villain isn't concentrating (ie. he's dead) will explode, collapsing the stone temple everyone is in, killing them (or creating a possibility of an adventure to find their way out from the tons of rock now atop them)?
In short, don't fight fair. Make 'em sweat, don't be breaking the rules, but use the rules and story to make the battle absolutely epic! Use a lot of descriptions of rooms (you'll be surprised how many spells and resources PCs will use to check out mundane stuff if you describe them well enough), create atmosphere (spider-webs and shed snake skins, corpses long dead (and fresh!), darkness, shadows, sounds echoing, smells of decay, trip-alarms... go to town.
This could be the battle of the players' lives!
