First, it does not dissolve into particles. These transparent pixels are an attempt to show how a 4D creature is cut off due to the limitations of 3D reality (however, it remains intact because its parts simply do not fit in 3D).
Secondly, I don't know if it's correct to call him an alien since he's from another dimension and not another planet.
And thirdly, it can be poisonous or eat representatives of 3D space. I guess it's like people eating paper with food on it. I don't think he would be delighted with such food.