Looking at the Mario series 2, Diddy Kong getting an amiibo in that line confuses me greatly.
There's currently no game that uses the Diddy amiibo for save data other than Smash.
The other two main games for amiibo save data with the Mario line (that I know of) are Mario Party 10 (amiibo Party Mode) and Mario Tennis: Ultra Smash.
Mario (and Dr. Mario, but he counts as Mario outside Sm4sh), Luigi, Peach, Bowser, Rosalina, Yoshi, Wario, and DK work for them both and Sm4sh (obviously).
Toad works with both, but not Smash.
Bowser Jr. works for Ultra Smash and Sm4sh.
So what of the new ones?
Waluigi and Daisy will work for Ultra Smash and (most likely) Mario Party 10.
Boo will work for Ultra Smash.
So why Diddy for series 2?
Why not Bowser Jr. like DK, Wario, and Rosalina?
Why not Toadette, who would theoretically work for both like Waluigi and Daisy?
Why not Spike, who would theoretically work for Mario Party 10's amiibo Party Mode?
Why not Dry Bowser or Sprixie Princess, who would work for Ultra Smash like Boo?