Rulings
Q1: What happens if a Digimon with 10 or fewer cards stacked with it is chosen for this card's On Play When Digivolving effect?
The top card is trashed until there are no more stacked cards. Once there is 1 card left, it isn't considered to have "stacked cards," therefore no more are trashed.
Q2: What happens if this card's On Play When Digivolving effect trashes stacked cards and the Digimon becomes a Digimon without DP?
It's trashed upon the rule check timing. This trashing isn't considered trashing from the battle area.
Q3: What happens if this card's On Play When Digivolving effect trashes stacked cards and the Digimon becomes an Option card?
It's trashed upon the rule check timing. This trashing isn't considered trashing from the battle area.
Data Sources
Lv.7 Shoutmon X7: Superior Mode BT21-030 R Mega | Data | Composite/Xros Heart/Blue Flare/Hero [Digivolve] Lv.6 w/[Hero] trait: Cost 5 When this card would be played, by placing 1 of your [Shoutmon] under it, reduce the play cost by 1 and cards in your trash can also be placed for DigiXros. [On Play] [When Digivolving] Trash the top 10 stacked cards of 1 of your opponent's Digimon. [When Attacking] [Once Per Turn] You may return 1 of your opponent's Digimon with no digivolution cards to the bottom of the deck. DigiXros -1: ∞ Digimon cards w/[Xros Heart] or [Blue Flare] trait & different card numbers
Lv.7 Shoutmon X7: Superior Mode BT21-030 R Mega | Data | Composite/Xros Heart/Blue Flare/Hero [Digivolve] Lv.6 w/[Hero] trait: Cost 5 When this card would be played, by placing 1 of your [Shoutmon] under it, reduce the play cost by 1 and cards in your trash can also be placed for DigiXros. [On Play] [When Digivolving] Trash the top 10 stacked cards of 1 of your opponent's Digimon. [When Attacking] [Once Per Turn] You may return 1 of your opponent's Digimon with no digivolution cards to the bottom of the deck. DigiXros -1: ∞ Digimon cards w/[Xros Heart] or [Blue Flare] trait & different card numbers
Lv.7 Shoutmon X7: Superior Mode BT21-030 R
Mega | Data | Composite/Xros Heart/Blue Flare
[Digivolve] Lv.6 w/[Hero] trait: Cost 3
When this card would be played, by placing 1 of your [Shoutmon] under it, reduce the play cost by 1 and cards in your trash can also be placed for DigiXros.
[On Play] [When Digivolving] Trash the top 10 stacked cards of 1 of your opponent's Digimon.
[When Attacking] {{OncePerTurn}} You may return 1 of your opponent's Digimon with no digivolution cards to the bottom of the deck.
DigiXros -1: ∞ Digimon cards w/[Xros Heart] or [Blue Flare] trait & different card numbers