You Can think about the a large panel of mirrors or lenses with variable reflecting/refracting index that can focus a large amount of Light at one place on variable distances. This can cause a huge damage on any creature when exposed to that focused energy.
Here is the Idea. Imagine a creature who are having some part in there body filled with some transparent liquid and they can vary the concentration of that liquid and can also give a different shapes( More similar to lanses i.e. concave or convex).
Now Working Principle of Lense is as
"A lens produces its focusing effect because light travels more slowly in the lens than in the surrounding air, so that refraction, an abrupt bending, of a light beam occurs both where the beam enters the lens and where it emerges from the lens into the air."
It also depends upon the material used for making the lense. For example refractive index of the water is 1.33 and for glass it is 1.62.More will be the refractive index of the material it will more bend the light. In other words you can say it is the bending capability of light.
In optics the refractive index or index of refraction n of an optical medium is a dimensionless number that describes how light, or any other radiation, propagates through that medium.
The point of discussion of refractive index is directly related to the concentraion of liquid that the creature will have. As creature is able to do modification in shape and Concentration of the liquid that creature will be able to bend light according to the choice and by this he can also focus it at whatever distance he want.
He can focus the light on some other animal or something for doing harm or for killing it.