Rulings
Q1: There are two of these cards in the Battle Area. Can I activate the Main effect of these two cards to play a card whose name contains "Sistamon" or "Gankumon" with the total play cost I pay -4?
No, you cannot. No. Main More than one effect cannot be activated at the same time.
Q2: If I use this card's Main effect to play "BT20-057 Gancumon", does it activate the first effect of "BT20-057 Gancumon" and the total play cost I pay is -6?
Yes, the total play cost to be paid is -6.
Q3: Cannot minus the play cost you pay, such as "ST12-03 Solarmon." Can I activate the Main effect of this card to play a card whose name contains "Sistamon" or "Gankumon" when a Digimon with the effect is in the Battle Area?
It can be activated and played, but the play cost is not minus.
Q4: BT9-047 Pormmon" and so on, "Cannot play Digimon under the effect." Can I activate the Main effect of this card to play a card with "Sistamon" or "Gankumon" in its name when a Digimon with the effect is in the Battle Area?
It can be activated, but it cannot be played.
Data Sources
Lv.4 BaoHuckmon BT20-013 C Champion | Data | Dinosaur [Main] [Once Per Turn] You may play 1 Digimon card with [Sistermon] or [Gankoomon] in its name from your hand with the play cost reduced by 2. --- Inherited: [Your Turn] All of your Digimon get +1000 DP.
Lv.4 BaoHuckmon BT20-013 C Champion | Data | Dinosaur [Main] [Once Per Turn] You may play 1 Digimon with [Sistermon] or [Gankoomon] in its name from your hand with the play cost reduced by 2. --- Inherited: [Your Turn] All of your Diigmon get +1000 DP.
Lv.4 バオハックモン BT20-013 C 成熟期 | データ種 | 恐竜型 【メイン】[ターンに1回]自分の手札から、名称に「シスタモン」/「ガンクゥモン」を含むデジモンカード1枚を支払う登場コスト-2で登場できる。 --- Inherited: 【自分のターン】自分のデジモン全てをDP+1000。