Nintendo 3DS
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Read+Write feature:
Write the character's stats to the amiibo to power up their illusory version.
Source: Mon Amiibo
Read-only feature:
Each individual figure or card summons different units, some much stronger than others.
This feature works with any amiibo (with the possible exception of those that work with its other features).
Source: Reddit user ibroussard / Thanks: memoryman3