Artemis was most recently seen in Young Justice. Great show! I am so pissed that they cancelled it! Unlike Commander Steel, I am 100% certain that Artemis is in season 3 of [Arrow](series:720988).
There are many ways she can be in the show.
1. For some reason, Olly finds out that Huntress has a younger half sister, unknown to Huntress herself. She is on the street for most of her life. Olly is in town one day and sees her doing vigilante stuff. Olly keeps a close eye on her and eventually decides to train her. She'll take the name Artemis.
2. They could do something completely weird and out of the blue and make Laurel become Artemis. Although I hear that she is supposed to be Black Canary.
3. She could be Olly's cousin and she is living with him. He notices that she is always coming home late so he decides to Arrow up and follow her one night. He sees that she is trying to be a crime fighter and she does have potential. The next night she is out, he is in costume and reveals himself and says he'll train her.
4. They'll blow our minds with something completely new and different.
Any other season 3 heroes or villains?