It was only a matter of time before hackers started tinkering with the insides that make up an Amiibo's data.
Right now it looks like Smash Bros. hackers like Mema Haxx are even figuring out how to get Amiibos that aren't actually announced/real yet into the game—like Duck Hunt, for example:
Okay, but that's just a bunch of menus. Do these fake Amiibos actually work? Yes! Take a look at this footage of a Game and Watch Amiibo being "imported" into the game:
The hacked Game and Watch Amiibo seems to work exactly like normal Amiibo do—it fights, it levels up and everything. Oh, and Game and Watch is also a character that doesn't have an actual physical Amiibo (yet).
Of course, 90% of the hype around Amiibos is the actual figurine. That said, with the healthy custom Amiibo modding scene that exists right now, perhaps its only a matter of time before we start seeing fake Amiibo figurines that actually work in Smash Bros., too.