Q1: What can be the target of De-Digivolve 1 in this card's End of Attack effect?
It targets 1 of your opponent's Digimon.
Q2: An effect suspended another Digimon when I attacked my opponent's Digimon using my Digimon with this card in its digivolution cards, and only my Digimon survived. Does this Digimon gain Piercing by this card's inherited effect and allow me to check my opponent's security stack?
No. You can't perform a security check even if you gain Piercing after deleting your opponent's Digimon in battle.
Lv.5 BlackRapidmon EX4-036 U Ultimate | Vaccine | Cyborg Digivolve: 3 from Lv.4 w/[Gargomon] in name or 2-color w/green <Alliance> (When this Digimon attacks, by suspending 1 of your other Digimon, this Digimon adds the suspended Digimon's DP and gains <Security Attack +1> for the attack.) [End of Attack] <De-Digivolve 1> (Trash 1 card from the top of 1 of your opponent's Digimon. Stop trashing when you would trash a level 3 card or the Digimon's last card) 1 of your opponent's Digimon. --- Inherited: [Your Turn] [Once Per Turn] When an effect suspends another Digimon, this Digimon gains <Piercing> for the turn.
Lv.5 BlackRapidmon EX4-036 U Ultimate | Vaccine | Cyborg Digivolve: 3 from Lv.4 w/[Gargomon] in name or 2-color w/green <Alliance> (When this Digimon attacks, by suspending 1 of your other Digimon, this Digimon adds the suspended Digimon's DP and gains <Security Attack +1> for the attack.) [End of Attack] <De-Digivolve 1> (Trash 1 card from the top of 1 of your opponent's Digimon. Stop trashing when you would trash a level 3 card or the Digimon's last card) 1 of your opponent's Digimon. --- Inherited: [Your Turn] [Once Per Turn] When an effect suspends another Digimon, this Digimon gains <Piercing> for the turn.
Lv.5 BlackRapidmon EX4-036 U Ultimate | Vaccine | Cyborg [Digivolve] Lv.4 w/[Gargomon] in name or Lv.4 2-color w/green: Cost 3 <Alliance> [End of Attack] <De-Digivolve 1> 1 of your opponent's Digimon. --- Inherited: [Your Turn] [Once Per Turn] When an effect suspends another Digimon, this Digimon gains <Piercing> for the turn.
Lv.5 ブラックラピッドモン EX4-036 U 完全体 | ワクチン種 | サイボーグ型 『名称に「ガルゴモン」を含むか緑を含む2色のLv.4』から3 ≪連携≫(このデジモンがアタックしたとき、他の自分のデジモン1体をレストさせることで、このアタックの間、このデジモンにレストさせたデジモンのDPをプラスし、≪セキュリティアタック+1≫を得る) 【アタック終了時】相手のデジモン1体を≪退化1≫(相手のデジモンに重ねられたカードを、上から1枚破棄する。進化元がなくなるか、Lv.3のデジモンになったらそれ以上破棄できない)。 --- Inherited: 【自分のターン】[ターンに1回]他のデジモンが効果でレストしたとき、このターンの間、このデジモンは≪貫通≫を得る。