Say you wanted the player to always be in the centre of the screen. Instead of giving the player the ScrollTo behaviour, I would give the behaviour to a separate object called Camera with an instance variable called something like 'ShakeY'. Every tick, set Camera position to Player.X,Player.Y+Camera.ShakeY. When you want to shake vertically, some how or other set the value of ShakeY to something random and crazy a few times then reset it back to 0. Easy!