One time only metamagics?

[winterwolf]

Just remembered...a potion of gaseous form would rock as an escape. He chugs that and then floats out past the adventurers...they can see him, but unless they have magic items (and get lucky) they can't hurt him...and if they do manage to kill them, they don't get much from the potion. It also gives them a chance to kill him. Also, I guarantee that any enemy who floats past them while they can't do anything (and the enemy will probably be chuckling all the while) will become the most hated foe of the party...nothing generates hate like mocking the party and getting away with it.
Other things would include some ring of tumbling (using the rules of wondrous item creation, a ring of tumbling would would cost 2500g for +5 or 10000g for +10) and if combined with boots of striding/springing (5500) makes a great getaway. In that case, the only people able to chase the BBEG down would be the monk or barbarian (or a psion with speed of thought).
BBEG would just have to get far enough away to be able to chug a potion of invis.
Or he could run far enough away to use a hat of disguise (and then pretend to be a weak underling the party might ignore while chasing after the BBEG).
Edit: put vest of tumbling, instead of ring of tumbling.

 

[winterwolf]

As a note, I used the table in the SRD dealing with creating magic items to figure out how much a rod of quicken spell (lesser) would cost with no maximum uses per day. The item turned out to be 58,333.33g. If the same rod were to be useable only once per day, this would become 11,666.66g. THis item is still pretty powerful, but you might balance that out by giving it a curse (maybe it deals 4pts of damage per level of the spell to be quickened, or maybe it "burns" up a spell of the level to be modified, as well as the spell to be modified). Both curses could conceivably knock a couple thousand g off of the final price.
In 3.0 you could modify items so that only one type of class could use them. You could apply that here (DM fiat) and state that only arcane or divine (depending on BBEG) can use the item. This used to drop 30% (i think) off of the price. The final price for the cursed, class-specific item would be around 7000g (good for a reward for any low level BBEG, and if it works right, the party won't even get it as a reward...).
Math:
Rod of quicken spell (lesser): 35000g (3 charges/day)
Bringing said item to 5 charges would mean dividing the 35000g by (3/5) or multiplying by (5/3) depending on which you find easier. This would bring the price of a lesser rod of quicken spell (lesser) up to 58333g.
Dropping the 5 charges per day to 1 charge per day means you divide the entire cost by 5, leaving it 11333g.
Take off the 1333g for a curse (a number I assigned arbitrarily, but fairly IMO) to make the item an even 10000. Take off another 30% to make the item specific to arcane or divine spells (or even a specific class) to leave the item at 7000g.
If the BBEG made the item himself, it would only cost him 3500g (and any BBEG that can't get ahold of 3500g shouldn't be a BBEG).