Rulings
Q1: If I don't have a level 4 or lower purple or yellow Digimon card in my trash, do both players still trash the top card of their security stack from this card's When Digivolving effect?
Yes, they do.
Q2: Do the Security effects on cards trashed by this card's When Digivolving effect activate?
No, they don't.
Q3: If I activate this card's When Digivolving effect when my opponent has an empty security stack, do I win the game?
No, just because there are no security cards to trash doesn't mean you win the game.
Q4: If either or both players have empty security stacks, can I use this card's When Digivolving effect to play a level 4 or lower purple or yellow Digimon card from my trash?
Yes, you can.
Q5: Does this card's When Digivolving effect trash one of each other's security from the top, even if there is no purple or yellow Lv.4 or lower Digimon card in my trash?
Yes, please trash.
Q6: Does the When Digivolving effect of this card activate the security effect that the card you trash has?
No, it does not activate.
Q7: If this card's When Digivolving effect is activated when the opponent has 0 security, does it win the game?
No, just because you cannot trash a security card does not mean you win the game.
Q8: If this card's When Digivolving effect is activated when I or my opponent or both have 0 security, can I still play a purple or yellow Lv.4 or lower Digimon card from my trash without paying cost?
Yes, you can play.
Q9: Which cards can be played by this card's When Digivolving effect?
One "Purple Lv.4 or lower Digimon card" or "Yellow Lv.4 or lower Digimon card".
Data Sources
Lv.6 Mastemon BT3-090 SR Mega | Vaccine | Angel [When Digivolving] Trash 1 card from the top of both players' security stacks. Then, play 1 purple or yellow Digimon card with a level of 4 or less from your trash without paying its memory cost.
Lv.6 Mastemon BT3-090 SR Mega | Vaccine | Angel [When Digivolving] Trash 1 card from the top of both players' security stacks. Then, play 1 purple or yellow Digimon card with a level of 4 or less from your trash without paying its memory cost.
Lv.6 Mastemon BT3-090 SR
Mega | Vaccine | Angel
[When Digivolving] Trash 1 card from the top of both players' security stacks. Then, you may play 1 {{Colour|purple}} or {{Colour|yellow}} Digimon card with a level of 4 or less from your trash without paying its memory cost.Lv.6 マスティモン BT3-090 SR 究極体 | ワクチン種 | 天使型 【進化時】お互いのセキュリティを上から1枚破棄する。その後、自分のトラッシュから、紫か黄のLv.4以下のデジモンカード1枚をコストを支払わずに登場できる。