1- Who will die?
Malcolm Merlyn of course. In a climatic fight with Oliver, he will get shot by an arrow. This of course will happen as he is one of the main antagonists of the series.
Edward Fyers will also get shot by an arrow. This time being special as Oliver will have just learned archery from Shado, the girl with the dragon tattoo.
Moira Queen will commit suicide paralleling her late husband's. It will be caused be her quilt of ruining the city, and be in front of an unmasked Oliver Queen.
Diggle will die trying to save Oliver. This will drive Oliver to kill Malcolm.
2- Who will change forever?
Tommy Merlyn will go to Nanda Parbat for training to avenge his father's death.
Roy Harper will become Arsenal to aid Oliver in saving the city.
3- What is the Undertaking?
I believe that the drug vertigo will be used like fear gas was in Batman Begins. It will be dispersed throughout the Glades using the abandoned subway system previously seen in the last episode. However, to cause more fear, Malcolm will put on his Dark Archer costume and cause the rest of the Glades to kill themselves with fear of death.
4- Who will be alluded to in the final moments?
Wintergreen. Maybe he can't die after all??
Ra's al Ghul when Tommy first goes to Nanda Parbat for training, he will bow to an unknown figure, who will then be shown to be Ra's.
Feel free to agree or disagree, and put down your predictions as well.