The phrase "like a shadow" conjures up images of something or someone following or being closely behind another. Synonyms for this phrase could include "shadowing" or "trailing" someone like a tail. Another phrase could be "in someone's shadow," indicating their influence or dominance over another. Other synonyms could be "hovering," "lurking," or "haunting" someone. One could also say that they are "dogging" or "stalking" someone like a predator. Overall, there are numerous synonyms that can be used to describe the idea of being like a shadow, each conveying a slightly different meaning or nuance.