Thea Queen joins Team Arrow as Speedy in season 4 of The CW supernatural series.Facebook/Arrow

"Arrow" fans can expect to watch a lot of changes in their favourite supernatural series when it returns on The CW with season 4, especially after Oliver Queen (Stephen Amell) and Felicity Smoak (Emily Bett Rickards) decided to quit Team Arrow in season 3.

Apart from Malcolm Merlyn's (John Barrowman) transformation as the new leader of League of Assassins and Thea Queen (Willa Holland) as Speedy, fans will also be introduced to a new set of villains.

Here are the four things that viewers need to know about "Arrow" Season 4:

Karl Yune to Reprise Maseo Yamashiro: The actor has teased about his return to the show as Maseo Yamashiro and said, "Mark has told me don't make any plans". However, Yune did not reveal whether his character will appear in flashbacks or he will be shown alive.

No Harley Quinn in Season 4: Actress Willa recently revealed that Harley Quinn will not be part of the series. "We had big plans for Harley. We got to see a little pigtail, the A.R.G.U.S. uniform and we just got rift away. If we could actually have Harley Quinn on the show then that would be amazing but that it is not gonna happen," said the actress.

H.I.V.E. to be Big Baddie: Actor David Ramsay revealed that H.I.V.E. will portray big baddie in upcoming season. "We are going to delve right into why H.I.V.E. hired Deadshot to kill Andy and what H.I.V.E. is all about to begin with. There will be a lot of Diggle's connection to H.I.V.E," he said.

Thea to Bring Back Oliver in Starling City: Earlier, Emily had stated that Oliver could be back in Starling city because of his sister, Thea. In a similar vein, Holland said during the MCM London Comic Con, "Thea would very much appreciate having her brother back in her life even though she is very happy that he is running off with the woman of his dreams right now. I think she definitely needs him too."