An NFC code isn't a creative work that can be copyrighted, and it's a stretch to call an NFC tag a DRM system. IANAL, but I suspect that Nintendo would have a hard time arguing in a court that aftermarket Amiibo cards are doing anything illegal at all (of course, provided those cards don't violate trademark or have copyrighted graphics/characters printed on them).

That's a dangerous game around these parts.

> I have no problem with people downloading a few hundreds bytes of data to unlock parts of software they already paid for.

I agree, the locked content is taking up storage space on their device and for many it's permanently inaccessible due to the scarcity of the cards.

Subtlety is lost in text, and wasted on the technically-minded.

> the locked content is taking up storage space

Modders noticed unknown amiibo codes in the Wii U version of Breath of the Wild version and were able to create tags months before the amiibos were actually released. So in this case the locked content is released earlier than designed.