Moving an entity with the mouse?

Easy solution.

guide = createpivot()

repeat

positionentity guide,0,0,0
rotateentity guide,0,entityyaw(camera),0
moveentity guide,mousexspeed(),0,mouseyspeed()

moveentity thingy,entityx(guide),0,entityz(guide)

until keyhit(1)

Anyway... totally untested but you get the idea.