Without a doubt Arrow has gone and given DC fans respect for the character of Green Arrow there is definitely a chance that in season 3 a number of big names have already been introduced including Deathstroke, Deadshot, Shrapnel, Bronze Tiger, The Huntress and even Nyssa Al Ghul. Here are some characters in my mind that will make appearances in Arrow season 3.
Steven R McQueen recently in an interview said he may have exaggerated his involvement with character but the idea isn't bad with the actions of McQueen. It doesn't seem likely with the low ranking on the list even with the Bludhaven Easter eggs in season 2.
Arrow has already used up a number of Batman characters such as Deathstroke and Bronze Tiger. It was revealed that in season two there will be a character named Seth that uses a drug to control people and mess with their minds. Sounds an awful lot like Scarecrow but where will he fit into all of this, for all we know Seth could just be a character made up by the show.
3. Ra's Al Ghul
We've already heard his name mentioned a lot of times on the show. Even the League of Assassins had multiple appearances and references in season 2 with links with Sara Lance and Malcolm Merlyn. With John Barrowman becoming a season regular in season 3 and with Ra's Al Ghul putting a price on his head the leader of the League of Assassins might just pay a visit to Starling.
4. Solomon Grundy
One of most bad ass villains in comic book history, Grundy has already sort of been introduced in the Arrow universe in the form of his alter-ego Cyrus Gold who was killed by the Arrow. Here's something interesting though, when he was killed an acid type substance hits his skin which makes it look like Solomon Grundy's skin, which means he could be brought back to life as Solomon Grundy.
5. Killer Frost
Caitlin Snow has already been introduced in Arrow as one of Barry's close friends and is a member of the select few who help Barry as the Flash in Central City. It may just only be a matter of time before her alter ego Killer Frost takes over.
6. The Flash
This is possibly the only one confirmed to make an appearance in season 3 of Arrow, with the first season of Flash and third of Arrow coinciding so a Green Arrow/Flash team up is inevitable.
7. The Blue Beetle
There has been a lot of speculation indicating that the character known as Daniel being introduced in season 3 could very well be the Blue Beetle. Because the character has been described as a rival vigilante who uses technology, it is most likely Blue Beetle.