Basq doesn't exist. He occupies a point in space--a single X,Y,Z point in the Cartesian plane, but he's not made of anything. People looking at him see whatever they want to see. Or what he wants you to see. Usually a mix. Just the same, he cannot be hurt swords or arrows. Only things that deal damage to an area (fireballs, gases) can damage him. Or weapons that can cut through an infinitely small point.
The PCs are invited to play in lumberjack games. They must see how quickly they can cut down a tree, how quickly they can use a great saw to cut a wheel from an already dropped tree, and must stay on top of a floating log while a lumberjack tries to roll the log to make them fall in the water. The winner gets beer and pancakes