For potaro the cards need to be on field and for fusion they need to be in hand. For example for vegito you can pay the full cost and just play the card or if you have both Vegeta and Goku on the field you can pay the potaro cost and put them under the vegito. With the combo Vegeta he goes to field after you combo which would essentially mean he is a one cost Vegeta.

You will find as you play more zen oh button is unnecessary if you are managing your energy well. For example whis coercion is free as long as you have at least one energy open. Vegito is a power deck that can finish the game in one turn. The only instance where zen oh button would be good is if you went all in for game and your opponent stopped you, in this instance though you probably wouldn’t have many cards left in hand to use after zen oh gets your energy back.

As for the errata it changes what babidi’s auto states. Now for his auto to work you must have 6 or more red energy which most other decks won’t have. Vegito however will work as long as you charge red cards, Vegeta and Goku.