You can not use any behaviors if you like. Create a sprite and make the image origin to the left.
Then give the sprite a variable called "w" and create an event like this:
--- sprite: add cos(self.angle)*500*dt - self.w*0.001
--- sprite: rotate self.w*dt degrees clockwise
"w" is the angular velocity of the object.
500 is the gravity. Change it to adjust the speed things go.
0.001 is the damping. Make it lower to allow the pendulum to swing longer before it stops.