yes
It is optional
You cannot get Shadow Mario as a playable character in Mario Superstar Baseball.
Because Shadow is a Soinc charter, not Mario.
Mario -luigi -Yoshi- peach --bowser-daisy-wario-waluigi-sonic-dr eggman-knuckles-tails-Amy-blaze-shadow-vector
No. it would be impossible for shadow Mario to be in every Mario game, because some Mario games came out before there was a shadow Mario, or even a luigi.
Shadow Mario is not entirely a regular Mario series character. He wasn't really his own character. Bowser Jr. is Shadow Mario.
no if you can get all this stars then you can play as luigi but not shadow Mario
Probaly shadow Mario he's like alot stonger
Shadow Mario first appered in Super Mario Sunshine, which came after Super Mario 64, so no.
No,you can not.
You can't. Simple as that.