Louie G.
Smash Legend
This has been my go-to for the time being, but I'm uncertain. I think Excitebiker lives on the edge a little bit. Unlike fellow 'retro' NES-era characters like Ice Climbers or Pit, Excitebiker is not a traditional protagonist. They are a faceless entity. In that respect perhaps they stride a bit closer to someone like Mr. Game & Watch. We scan for every and any possibility, so Excitebiker isn't too weird to us, but I don't think they're someone who immediately comes to mind to the general public. But despite this, maintains a strong level of notoriety not unlike Duck Hunt.Would Excitebiker count as a surprise character?
I think Duck Hunt is probably the closest point of comparison here. On the off chance that we speculated on Duck Hunt Dog / "Mr. Peepers" here back in 2013 or whenever, this was deemed as the game's potential retro pick. Duck Hunt was classified alongside Ice Climber or Kid Icarus. I think to most of us, Wii Fit Trainer felt like the WTF or "hardware" character which was a budding term at the time, until Sakurai clarified that it was in fact Duck Hunt who fulfilled the surprise role. So yeah on surface level Excitebiker doesn't seem like a surprise character, but perhaps it still would be. Duck Hunt wasn't completely unpredictable, it was just an unorthodox fighter with a novel execution. Excitebiker would achieve the same niche, arguably.
But the real answer is a bit of a copout - he counts if Sakurai says he counts. That's it really, his intent behind the addition is the only criteria. Something that was clarified with Duck Hunt and Piranha Plant and is otherwise just kind of self-evident for Mr. G&W and ROB. Would Excitebiker count? We'd just have to wait for him to tell us that he does, or use process of elimination if nobody else is particularly out of the ordinary I suppose.