#1 Roman Reigns

To be honest, the one match that Goldberg is more than likely to have at Super ShowDown would be against Roman Reigns. As mentioned earlier, the never-ending feud between him and King Corbin is finally over. Also, Reigns is probably the most worthy name that Goldberg could call out on Friday Night SmackDown.
These two had an intense face-off a while back but never got around it. This is the time for the match to happen. The Big Dog, himself, needs to fill out his pay-per-view gap between Royal Rumble and his inevitable Universal Title match against The Fiend at WrestleMania.
Did you know a top WWE Superstar just wrestled outside the company? More details HERE
This is also the only Goldberg match that has been actively teased, with the two sharing a Twitter exchange born out of a simple doubt from Cultaholic's Sam Driver, regarding Reigns' entrance. This might lead to a dream match between the two masters of the Spear.
This could be an all-out brawl likely to last between 5 to 10 minutes, which would suit Goldberg perfectly. Roman Reigns is also at his best in these situations where there is non-stop action, as long as a story is in place.
Expect this to be the main event of Super ShowDown 2020. Hopefully, the Big Dog will get a good match out of the WCW legend.