Originally Posted by protocida
Cupid is obssesed with Oliver and his enemies.
Shado has her own personal vendetta against corrupt types.
Unless Cupid knew that Arrow is especifically targeting "The List", she would have no reason to go after its members.
It's only certain individuals and as such, she has a 'list' of her own. Where as the synopsis made a point to specifically note that the targets were the same as Oliver's; which was what made me think it was Cupid in the first place. Moreover, while both characters use arrows, the implication of the summary made it sound as if there was a copycat on the loose or that the crimes would be misattributed to Arrow; which again strikes me more of Cupid and Shado.
Another count against Shado is that the show would have only very recently featured Huntress; who is also the daughter of a member of organised crime who has now dishing out vigilante justice. While not exactly the same, their back stories are similar enough that I don't think the creators would deliberately want to have them both appear so close to one another.