Starter or Unlockable?

Some of us wonder why some characters are unlockable or starter, lets figure out how it works. Then we can figure out which characters could appear as unlockables.

Some characters appear as unlockables due to a few reasons:
-Obscurity
-Popularity


I'll list the characters that could be unlockable or starter. It's going to be pretty long.
I will just list this, since they need no reason why they will be starters.
Automatic Starters:
-Mario
-Link
-Kirby
-Samus
-Pikachu
-Samus
-Fox
-Yoshi...

Starter or Unlockable?