On the Nintendo 3DS system players can collect other Miis via StreetPass and then visit and view them in the StreetPass Mii Plaza. But it turns out that many more Miis will show up in the plaza and they arrive by other means... perhaps by way of SpotPass (local wi-fi), though on this I am not sure.
What I'm curious to know is what are the ways for Miis to arrive at StreetPass Mii Plaza by Invitation?
These are the ones without any hats or costumes way in the back, and when you select on them they give no information except for a message - "Met via Invitation."
They don't show up at the gate to meet your Mii either.