Thanks to A for the heads up. You can watch the entire Facebook Video here which TVLine used to make a summary of the main points from.
Amell also teased a “slightly modified version” of the Arrow costume, plus an appearance by “someone that we haven’t seen in two full seasons. So there’s that.” (Before you blurt out, “Sla-a-a-a-ade!!!,” remember that he popped up midway through Season 3.)
Fielding a flurry of other questions, Amell had “no comment” on any Legends of Tomorrow characters appearing in Arrow‘s premiere (which he summed up with the word “legacy”); shared his enthusiasm for The Flash‘s Season 3 premiere title, then said the “Flashpoint” storyline “certainly could” affect Arrow; and when asked, “What about Olicity?,” he playfully hedged, “What about it…?”