Q1: Which cards can be played by this card's When Attacking effect?
The cards that can be played by this card's When Attacking effect are "Blue Lv.3 Digimon cards" or "Tamer cards".
Lv.5 Mermaimon BT18-027 C Ultimate | Data | Aquabeast [When Attacking] You may play 1 blue level 3 Digimon card or 1 Tamer card from this Digimon's digivolution cards without paying the cost.
Lv.5 Mermaimon BT18-027 C Ultimate | Data | Aquabeast [When Attacking] You may play 1 blue level 3 Digimon card or 1 Tamer card from this Digimon's digivolution cards without paying the cost.
Lv.5 Mermaimon BT18-027 C Ultimate | Data | Aquabeast [When Attacking] You may play 1 blue level 3 Digimon card or 1 Tamer card from this Digimon's digivolution cards without paying the cost.
Lv.5 マーメイモン BT18-027 C 完全体 | データ種 | 水棲獣人型 【アタック時】このデジモンの進化元から、青のLv.3のデジモンカード1枚かテイマーカード1枚をコストを支払わずに登場できる。