Q1: Does this card’s When Digivolving effect force both players to trash the top 2 cards of their decks?
Yes. Both players must trash 2 cards each, if possible.
Q2: Can I choose to not return the cards to my hand for this card's When Digivolving effect when I have 1 Guilmon or 1 card with {{EffectLinkArchetype|Growlmon|Gallantmon}} in my trash?
Yes, the effect reads ""you may return ... to your hand,"" therefore you may choose to not return cards to your hand. However, even in such cases, both players must trash 2 cards from the tops of their decks.
Lv.4 BlackGrowlmon EX4-008 U Champion | Virus | Dark Dragon [When Digivolving] Trash the top 2 cards of both players' decks. Then, you may return 1 [Guilmon] or 1 card with [Growlmon] or [Gallantmon] in its name from your trash to your hand. --- Inherited: [On Deletion] You may return 1 [Guilmon] or 1 card with [Growlmon] or [Gallantmon] in its name from your trash to your hand.
Lv.4 BlackGrowlmon EX4-008 U Champion | Virus | Dark Dragon Digivolve: 2 from Lv.3 w/[Guilmon] in name [When Digivolving] Trash the top 2 cards of both players' decks. Then, you may return 1 [Guilmon] or 1 card with [Growlmon] or [Gallantmon] in its name from your trash to your hand. --- Inherited: [On Deletion] You may return 1 [Guilmon] or 1 card with [Growlmon] or [Gallantmon] in its name from your trash to your hand.
Lv.4 BlackGrowlmon EX4-008 U Champion | Virus | Dark Dragon {{DigivolveFromArchetypes|2|3|Guilmon}} [When Digivolving] Both players trash the top 2 cards of their decks. Then, you may return 1 [Guilmon] or 1 card with [Growlmon] or [Gallantmon] in its name from your trash to your hand. --- Inherited: [On Deletion] You may return 1 [Guilmon] or 1 card with [Growlmon] or [Gallantmon] in its name from your trash to your hand.
Lv.4 ブラックグラウモン EX4-008 U 成熟期 | ウィルス種 | 魔竜型 【進化時】お互いのデッキの上から2枚破棄する。その後、自分のトラッシュから、「ギルモン」か名称に「グラウモン」か「デュークモン」を含むカード1枚を手札に戻せる。 --- Inherited: 【消滅時】自分のトラッシュから、「ギルモン」か名称に「グラウモン」か「デュークモン」を含むカード1枚を手札に戻せる。