War, or at least skirmishes, have broken out in a small region. The local baron contacts the party, and arranges for the safe transport of his only remaining family, a teenaged daughter that he dotes upon, Jada, to the capital. A simple quest, the party must only get her to the capital, and present her to the Baron’s representative at court. Easy money for any group of seasoned adventurers.
Except… it’s not. Jada is not exactly the typical noble’s brat. In addition to the stereotypical character flaws, she is also addicted to ‘Fairy Dust’(or other hallucinogen of the DM’s choice), and she’s not going to give it up for a little trip voluntarily, even if she could. During the journey, she will be the greatest hazard to the adventurers: She will imagine nonexistent threats, and react accordingly, and independently, fleeing from illusionary creatures, assaulting party members as if bandits. She will consider real threats non-extant, trying to walk over bridges that don’t exist, running to the arms of bandits or enemy soldiers, etc.
At the DM’s discretion, Fairy Dust may enhance the magical or psychic abilities of the imbiber, enough for her to lend her twisted vision of the world to another person, a kind of waking nightmare. It may also lend her the luck to be unharmed by the reality that underlies her vision, though the adventurers should have no such protection.
If the adventurers catch her imbibing the drug, they may be able to take it away, in which case they will have to deal with physical withdrawl symptoms within the day. These should include a great deal of pain, writhing, screaming, and general inability to be moved for several days.
Should the PCs indulge, make up a lot of fancy things for them to ‘see’. And addict them after the second/third time. Jada only has enough for one person to make the trip plus a few days supplies, since she knows she can get more in the capital.
Reward upon reaching the capital should be adequate for the undrugged version of the walk. To complicate things, the adventurers may have to prove the addiction a pre-existing condition to keep from getting blamed for it!