When Yoda you deploy, under any Jedi Padawan, one copy of Yoda stack you can. On top of that stack, Yoda can't be. 1 extra card in it, the stack can have. Count as Yoda this card does not while stacked under a Padawan.
You may have multiple copies of Yoda (G) stacked on different Padawns.
Other versions of Yoda can be played legally while Yoda (G) is stacked beneath a Jedi Padawan.
Yoda (G) can't leave the stack once stacked.
Yoda's ability is not in effect during setup (as with all cards). If you play it during setup, you spend 3 for a Yoda that can't be stacked with a padawan.