We may have a clue as to the return of Oliver Queen in Arrow.
Stephen Amell posted the following fan art image of what looks to be Ollie rising out of the Lazarus Pit.
The Lazarus Pit, in the comics, was discovered by Ra's Al Ghul, which has restorative properties.
If you paid close attention to the mid-season finale of Arrow, you heard Ra's Al Ghul mention that he has been killing people for 60 odd years, which hints that he has been using the Lazarus Pit himself.
"Arrow" returns Wednesday, January 21st at 8pm ET on the CW.