Rulings
Q1: What does "declare 1 card category" in this card's Start of Opponent's Turn effect mean, exactly?
It refers to the four card categories: Digi-Egg cards, Digimon cards, Tamer cards, and Option cards. You declare 1 of these categories at the start of your opponent's turn for this card's effect, your opponent reveals the top card of their deck, and if the revealed card is in the declared category, this Digimon will be unaffected by effects from cards in the declared card category.
Q2: Can this card's Start of Opponent's Turn effect declare card categories that do not go into the deck, such as Digi-Egg cards?
Yes, it can be declared.
Q3: I declared Tamer cards for this card's Start of Opponent's Turn effect, and a Tamer card was revealed from the deck. In such cases, is this Digimon unaffected by inherited effects on Tamer cards in digivolution cards of my opponent's Digimon?
No, it's affected by such effects. Inherited effects on Tamer cards in digivolution cards of Digimon are treated as Digimon effects.
Q4: I declared Digimon cards for this card's Start of Opponent's Turn effect. If a Digimon card is revealed from the deck, is this Digimon unaffected by Security effects activated by Security Digimon?
Yes, it isn't affected. Security effects on Security Digimon are treated as Digimon effects, so the "this Digimon isn't affected by the effects of your opponent's Digimon" effect prevents such effects from affecting this Digimon.
Q5: Can I use this card's When Digivolving effect to return my EX2-007 Mother D-Reaper from the battle area to the security stack, reveal all cards in my opponent's security stack, and place 1 card among them at the top of my opponent's deck?
Yes, you can. If your EX2-007 Mother D-Reaper is chosen as the target to place in the security stack, it will ultimately be placed at the bottom of the Digi-Egg deck instead of the security stack according to the rules, but it meets this card's "by placing 1 Digimon on top of its owner's security stack" condition. A card isn't actually added to the security stack, therefore effects such as "when a card is added to the security stack" don't trigger.
Q6: Can I use this card's When Digivolving effect to return my token played as a Digimon from the battle area to the hand, reveal all cards in my opponent's security stack, and place 1 card among them at the top of my opponent's deck?
Yes, you can. If your token is chosen as the target to place in the security stack, it will ultimately be removed from the game instead of being placed in the security stack according to the rules, but it meets this card's "by placing 1 Digimon on top of its owner's security stack" condition. A card isn't actually added to the security stack, therefore effects such as "when a card is added to the security stack" don't trigger.
Q7: If I choose my EX2-007 Mother D-Reaper or token that is treated as a Digimon in the battle area as the target for this card's When Digivolving effect, it isn't placed in the security stack. In such cases, do "when a card is removed from the security stack" effects trigger because a card wasn't added to the security stack even though it normally should have been added?
No, it doesn’t trigger.
Q8: Due to this card's Start of Opponent's Turn effect, this card no longer gets Digimon effects. At this time, does it no longer get the inherited effects of Digimon cards in this card's digivolution sources?
No. It gains inherited effects.
Q9: Due to this card's Start of Opponent's Turn effect, this card is no longer affected by Digimon effects. At this time, is this card not affected by the effects of my other Digimon?
Yes, it is not affected by them.
Data Sources
Lv.6 Quantumon LM-020 SEC Mega | Data | Fairy [When Digivolving] By placing 1 Digimon on top of its owner's security stack, reveal all of your opponent's security cards, and place 1 card among them on top of your opponent's deck. Shuffle the rest and return them to the security stack. [Start of Opponent's Turn] Declare 1 card category. Then, reveal the top card of your opponent's deck. If that card is of the declared category, this Digimon isn't affected by the effects of that card category for the turn. Return the revealed card to the top or the bottom of your opponent's deck.
Lv.6 Quantumon LM-020 SEC Mega | Data | Fairy [When Digivolving] By placing 1 Digimon on top of its owner's security stack, reveal all of your opponent's security cards, and place 1 card among them on top of your opponent's deck. Shuffle the rest and return them to the security stack. [Start of Opponent's Turn] Declare 1 card category. Then, reveal the top card of your opponent's deck. If that card is of the declared category, this Digimon isn't affected by the effects of that card category for the turn. Return the revealed card to the top or the bottom of your opponent's deck.
Lv.6 Quantumon LM-020 SEC Mega | Data | Fairy [When Digivolving] By placing 1 Digimon on top of its owner's security stack, reveal all of your opponent's security cards, and place 1 card among them on top of your opponent's deck. Shuffle the rest and return them to the security stack. [Start of Opponent's Turn] Declare 1 card category. Then, reveal the top card of your opponent's deck. If it's of that category, this Digimon isn't affected by that category's effects, other than this Digimon's effects, for the turn. Return the revealed cards to the top or bottom of your opponent's deck.
Lv.6 クオンタモン LM-020 SEC 究極体 | データ種 | 妖精型 【進化時】デジモン1体を持ち主のセキュリティの上に置くことで、相手のセキュリティ全てをオープンし、その中から1枚を相手のデッキの上に置く。残りはシャッフルしてセキュリティに戻す。 【相手のターン開始時】カードカテゴリー1つを宣言する。その後、相手のデッキの上から1枚オープンし、そのカードが宣言したカードカテゴリーなら、ターン終了まで、このデジモンは宣言したカードカテゴリーの効果を受けない。オープンしたカードは相手のデッキの上か下に戻す。