Sami Zayn actually appeared on SmackDown just before the main event, but he declined to cut a promo, telling the fans in attendance that they're "not worth it." However, the Underdog from the Underground returned once the show went off the air.
While Zayn was doing his new anti-smark shtick, he was joined in the ring by his old frenemy Kevin Owens. At first KO acted like he was happy to see Zayn and raised his hand, but this quickly led to a Stunner (a move Owens has now adopted as his finisher).
It's interesting to see this dynamic between Owens and Zayn, who have usually ended up on opposite ends of the heel/face spectrum throughout their careers. Chances are this was just a one-off, though, as it's hard to imagine WWE setting up yet another feud for these guys.