Don't use Physics together with other non-physics movement behaviors like MoveTo and Rotate, they are not compatible and will be conflicting with each other, causing weird bugs.
I made some changes to your project, take a look:
dropbox.com/s/r270h45hgrifpxs/bouncyboss.c3p
Pay attention to collision polygons, the polygon on Boss sprite was completely messed up.
Because the boss is a line it doesn't reflect from walls well.
You can try to further improve this by adjusting reflection angles, for example using raycasting feature of the Line Of Sight behavior. Before the collision with walls, cast a ray, save its reflection angle in a variable. On collision use this saved reflection angle value to set new velocity x and y. But it may be a difficult task, since the boss can hit two different walls with its two ends...