Read-only feature:

Play as Shadow Mewtwo before unlocking it in-game

Read-only feature:

Receive a random title, customization option, or gold

Once a day per amiibo, up to five times per day total. The customization options and titles received this way are amiibo-exclusive (they can't be obtained by other means).

This feature works with any amiibo (with the possible exception of those that work with its other features).

Source: / Thanks: Boblers