Team Arrow is in need of some rebuilding work.
Season 4 saw the group go in a whole host of different directions, with Thea on the outs from vigilante life, and Diggle rejoining the army in an attempt to find himself.
Then there's the death of Laurel Lance, meaning the team was already one member down permanently (ish, anyway, since Katie Cassidy is still going to be around as an Arrowverse regular), while just outside of that, Quentin Lance had to leave the SCPD, meaning he was without a real position on the show.
With just Oliver and Felicity left in the Arrowcave (and even then they're somewhat apart), Ollie having a new role as Mayor, and some villainous voids to be filled, the show needs to replenish its stock entering its fifth season.
Thankfully, it seems to be going about doing exactly that. With filming well underway ahead of the show's October return, we've already got a number of castings and characters, and these are the new additions you need to know about.