The upcoming episode of "Arrow" season 6 will highlight the much-awaited showdown between Oliver Queen (Stephen Amell) and the series' current big bad, Ricardo Diaz (Kirk Acevedo). The villain has worked hard in the last few episodes to match the power and influence of the Star City mayor, but the fate of the citizens might ultimately depend on the outcome of Oliver's one-on-one combat with Diaz.

"Arrow" season 6 episode 20 is titled "Shifting Allegiances," and according to the latest promo released by The CW, a bloody brawl between Oliver and Diaz will ensue. The episode will show Oliver accepting Diaz' proposal on how the two of them can settle their issues. The villain will propose a combat, and whoever will lose must leave Star City and never go back. This could be the chance for Oliver to banish his enemy once and for all, assuming that Diaz' will stay true to his words.

Unfortunately, the Episode 20 teaser suggests that Diaz will have the upper hand of the battle, and the villain will ultimately take Oliver as his hostage. On the other hand, the next chapter of "Arrow" season 6 will show Oliver asking help from his friend, Quentin (Paul Blackthorne), as he prepares for his final fight against Diaz. Quentin will be sensing Oliver's fear, thus making him take a more aggressive approach to train his friend.

To recap the previous episode of "Arrow" season 6, Diaz and Black Siren (Katie Cassidy) requested aid from a powerful underground organization in the showdown against Oliver. The viewers were also able to get a glimpse of Diaz' troubled past, explaining how the character became a cunning and callous person that he is now. 

Meanwhile, Rene (Rick Gonzalez) will struggle to adjust after being discharged from the hospital. It will be business as usual for the character, although taking on the role of Wild Dog once again in the new Team Arrow will be quite challenging. 

"Arrow" season 6 episode 20 will air on Thursday, April 26 at 9 p.m. ET on The CW.