In my next D&D session I run (which is in the Dark Sun setting), the PC's will be boarding a sand skiff and venturing out into the desert. I have planned for on their way, they get attacked by tribal people riding giant worms (Dune, anyone?) and have to fend them off. What I have planned right now, is that in order to fend off the worms, the PC's have to jump from the sand skiff onto the worms, and then beat through its armor, and then attack its soft flesh beneath while fending off the worm's handlers.
They can tether themselves to the sand skiff, but that limits their mobility. While there's an NPC there to do it, the PC's can (if they wish) drive the sand skiff, manipulating the sails to alter speed and direction (there's a primal wind/sand spirit helping them, so don't worry about that). The skiff has a certain amount of HP, and they can ram the worms for damage, but also lose that much HP of the skiff.
During the race, there will be obstacles and terrain that they can attempt to use to their advantage. Rocky outcroppings, large dunes, etc. That they can choose to steer into to get an advantage, but possibly at the expense of their skiff's HP.
I'm thinking of giving them a finite supply of thumper-charges that distract the worms, explosives, and various other throwable things or useable items to make the fight more interesting.
I'm going to work the entire encounter by drawing nothing on the map itself, but rather having physical, moveable objects represent terrain and such- I even made a sand skiff shape out of cardboard, paperclips, and tape that will represent the PC's sand skiff.
Does anyone have any suggestions or ideas? Any resources?