Wow, I was mistaken. I thought Nintendo was being just greedy, but this is disgusting. More info on Mario Party 10 and amiibo support: http://www.nintendo.com/amiibo/line-up/#/mario_party.
Emphasis added by me. So amiibo Party in Mario Party 10 not only requires at least one amiibo, but the game board you play in depends on the amiibo used. So you need even more amiibo just to play this mode properly. (Which arguably seems like the best mode in the game as it doesn't have that awful vehicle from Mario Party 9 and looks like a watered down classic Mario Party mode.)Your amiibo becomes a game piece in the all-new amiibo Party mode! At least one amiibo is required in order to access this mode.
Game boards vary based on the amiibo used. On the Mario board, you might encounter an event where you use a Mushroom to suddenly grow or collect coins while defeating your rivals. On the Luigi board, you may have to suck up your rivals' stars and coins using the Poltergust.