

Q1: Can I return just 2 cards from the trash to the deck for the condition of this card's 1st effect?
No, you can't. A "by" condition can't be met if only some of the required actions are performed. The conditions for the 1st effect require you to return the specified number of cards to the deck.
Lv.6 Gankoomon BT23-057 R Mega | Data | Holy Warrior/Royal Knight/CS When this card would be played, by returning 3 cards with [Huckmon], [Sistermon] or [Jesmon] in their names from your trash to the top or bottom of the deck, reduce the play cost by 5. [On Play] [When Digivolving] You may play 1 [Hinukamuy] Token. (Digimon/White/6000 DP/<Alliance><Reboot><Blocker>) Then, delete 1 of your opponent's Digimon with a play cost of 6 or less. For each of your other Digimon, add 3 to this effect's play cost maximum. ---
Lv.6 Gankoomon BT23-057 R Mega | Data | Holy Warrior/Royal Knight/CS [Digivolve] Lv.5 w/[CS] trait: Cost 3 When this card would be played, by returning 3 cards with [Huckmon], [Sistermon] or [Jesmon] in their names from your trash to the top or bottom of the deck, reduce the play cost by 5. [On Play] [When Digivolving] You may play 1 [Hinukamuy] Token. (Digimon/White/6000 DP/<Alliance><Reboot><Blocker>) Then, delete 1 of your opponent's Digimon with a play cost of 6 or less. For each of your other Digimon, add 3 to this effect's play cost maximum. --- -
Lv.6 Gankoomon BT23-057 R mega | Data | Holy Warrior/Royal Knight/CS [Digivolve] Lv.5 w/[CS] trait: Cost 3 When this card would be played, by returning 3 cards with [Huckmon], [Sistermon] or [Jesmon] in their names from your trash to the top or bottom of the deck, reduce the play cost by 5. [On Play] [When Digivolving] You may play 1 [Hinukamuy] Token. (Digimon/White/6000 DP/<Alliance><Reboot><Blocker>) Then, delete 1 of your opponent's Digimon with a play cost of 6 or less. For each of your other Digimon, add 3 to this effect's play cost maximum.
Lv.6 ガンクゥモン BT23-057 R 究極体 | データ種 | 聖騎士型/ロイヤルナイツ/CS このカードが登場するとき、自分のトラッシュから、名称に「ハックモン」/「シスタモン」/「ジエスモン」を含むカード3枚をデッキの上か下だけに戻すことで、支払う登場コスト-5。 【登場時】【進化時】「ヒヌカムイ」(デジモン• 白• DP6000• ≪連携≫≪再起動≫≪ブロッカー≫)トークン1体を登場できる。その後、登場コスト6以下の相手のデジモン1体を消滅させる。他の自分のデジモン1体ごとに、この効果の登場コスト上限+3。 ---