Yea, i found that out last night.  I hadnt gotten enough of the shines
from the park.  Once i got Yoshi (and i already had 30 shines) each of
the shadow mario's appeared each time the game saved.
I had read that shadow mario was supposed to show up after 25, and 30
shines, but i had 27 already, and he hadnt shown up. Which is why i
asked.  I didnt know i had to complete a certain stage to get yoshi, to
get the shadow mario's to show their face.

Thanks.