Q1: "I used this card's On Play effect to give 1 of my opponent’s Digimon with the lowest level ""When Attacking Lose 2 memory."". Then, that opponent's Digimon digivolved and another Digimon became their Digimon with the lowest level. What happens to the ""When Attacking Lose 2 memory"" effect?"

Your opponent's target Digimon that was specified when the effect activated will continue to have the "When Attacking Lose 2 memory" effect until the end of your opponent's turn.

Data Sources

Official English Card Listworld.digimoncard.com

Lv.4 MailBirdramon      EX4-018  C
Champion | Data | Machine/Blue Flare

[On Play] 1 of your opponent's Digimon with the lowest level gains "[When Attacking] Lose 2 memory" until the end of your opponent's turn.
[On Deletion] <Save> (You may place this card under one of your Tamers.)

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Inherited: <Jamming> (This Digimon can't be deleted in battles against Security Digimon.)

Official English (Asia) Card Listen.digimoncard.com

Lv.4 MailBirdramon      EX4-018  C
Champion | Data | Machine/Blue Flare

[On Play] 1 of your opponent's Digimon with the lowest level gains "[When Attacking] Lose 2 memory" until the end of your opponent's turn.
[On Deletion] <Save> (You may place this card under one of your Tamers.)

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Inherited: <Jamming> (This Digimon can't be deleted in battles against Security Digimon.)

DCG Wikidigimoncardgame.fandom.com

Lv.4 MailBirdramon      EX4-018  C
Champion | Data | Machine/Blue Flare

[On Play] 1 of your opponent's Digimon with the lowest level gains "[When Attacking] Lose 2 memory." until the end of your opponent's turn.
[On Deletion] <Save>.

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Inherited: <Jamming> (This Digimon can't be deleted in battles against Security Digimon.)

Official Japanese Card Listdigimoncard.com

Lv.4 メイルバードラモン      EX4-018  C
成熟期 | データ種 | マシーン型/ブルーフレア

【登場時】次の相手のターン終了まで、最もLv.の低い相手のデジモン1体に「【アタック時】メモリー-2。」の効果を与える。
【消滅時】≪セーブ≫（このカードを自分のテイマーの下に置ける）

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Inherited: ≪ジャミング≫（このデジモンはセキュリティデジモンとのバトルでは消滅しない）

Rulings

Data Sources

Japanese Rulings