Rulings
Q1: If EX5-070 X Antibody Proto Form is in this Digimon's digivolution cards, this Digimon would be deleted, and EX5-070 X Antibody Proto Form's inherited effect places it on top of my security stack, does this Digimon's On Deletion effect activate?
No, it doesn’t activate. EX5-070 X Antibody Proto Form's inherited effect will trigger/activate "when this Digimon would leave the battle area other than by one of your effects," but since EX5-070 X Antibody Proto Form isn't in this Digimon's digivolution cards at the time of activation of the On Deletion effect because it's placed in your security stack before this Digimon is deleted, the "if X Antibody was in this Digimon's digivolution cards" condition isn't met, so the effect doesn't activate.
Data Sources
Lv.5 Myotismon (X Antibody) P-145 P Ultimate | Virus | Undead/X Antibody [Digivolve] [Myotismon]: Cost 0 [On Play] [When Digivolving] Delete 1 of your opponent's level 4 or lower Digimon. [On Deletion] If [Myotismon] or [X Antibody] was in this Digimon's digivolution cards, you may play 1 level 6 Digimon card with [Myotismon] in its name from your trash without paying the cost.
Lv.5 Myotismon (X Antibody) P-145 P Ultimate | Virus | Undead/X Antibody [Digivolve] [Myotismon]: Cost 0 [On Play] [When Digivolving] Delete 1 of your opponent's level 4 or lower Digimon. [On Deletion] If [Myotismon]/[X Antibody] is in this Digimon's digivolution cards, you may play 1 level 6 Digimon card with [Myotismon] in its name from your trash without paying the cost.
Lv.5 Myotismon (X Antibody) P-145 P Ultimate | Virus | Undead/X Antibody [Digivolve] [Myotismon]: Cost 0 [On Play] [When Digivolving] Delete 1 of your opponent's level 4 or lower Digimon. [On Deletion] If [Myotismon] or [X Antibody] was in this Digimon's digivolution cards, you may play 1 level 6 Digimon card with [Myotismon] in its name from your trash without paying the cost.
Lv.5 ヴァンデモンX抗体 P-145 P 完全体 | ウィルス種 | アンデッド型/X抗体 「ヴァンデモン」:コスト0 【登場時】【進化時】Lv.4以下の相手のデジモン1体を消滅させる。 【消滅時】このデジモンの進化元に「ヴァンデモン」/「X抗体」があったなら、自分のトラッシュから、名称に「ヴァンデモン」を含むLv.6のデジモンカード1枚をコストを支払わずに登場できる。