That and ARMS got an entire set of months dedicated to getting people to talk about the game. "Guess that character" is a pretty big way to promote it, with a demo at the end.
They don't do that much at all otherwise for Smash. There's of course a few promotional characters(as in to directly advertise the latest game, though not the sole reason they're in), but nobody was handled the way ARMS was. Hell, I'd say ARMS was the biggest way of advertising a game. In an ironic twist, Min MIn wasn't used to advertise it so much as the game was used to advertise an option for Smash.
There's also a timing thing that makes it different from other advertisement options. From what we have data on, it's likely Min Min was determined almost a year before her original release. That means that they'd have to have thought of this guessing game and implement it in January, knowing she would take a massively long time enough to justify it. I'd say that hardly adds up. To me, she wasn't there for advertising anything but they had to have an excuse to throw in some Smash news to keep the ball rolling. The gameplay delays suggest she was just a month later than normal, I doubt she would've been ready by March. May, sure, if the delay didn't happen.
...I'm a bit tired, so I may have worded that oddly.