Rulings
Q1: Do I choose 1 Digimon with the lowest play cost or 1 Tamer with the lowest play cost to delete for "among your opponent's Digimon and Tamers, delete 1 with the lowest play cost" in this card's When Attacking effect?
No. You delete the one with the lowest play cost from among your opponent's Digimon and Tamers. If multiple Digimon and/or Tamers have the lowest play cost, the player of this card chooses from among them.
Q2: I used this card's When Attacking effect to trash 2 level 6 or higher digivolution cards. If my opponent has 1 Digimon with a play cost of 3 and 1 Digimon with a play cost of 4, can I delete both of them?
Yes, you can. For every level 6 or higher digivolution card trashed, this effect deletes 1 of your opponent's Digimon or Tamers in order starting with the lowest play cost.
Q3: If I use this card's When Attacking effect to trash 3 level 6 or higher digivolution cards, do I trash the top 2 cards of my opponent's security stack after deleting 3 of their Digimon and/or Tamers with the lowest play costs?
Yes, that's correct.
Q4: Can I use this card’s When Digivolving effect to choose 0 for the play cost total without deleting an opponent's Digimon?
No, you can't. This effect requires you to choose at least 1 of your opponent's Digimon with a play cost of 6 or less whenever possible.
Data Sources
Lv.7 Omnimon Alter-B EX4-073 SEC Mega | Virus | Holy Warrior Digivolve: 2 from Lv.7 w/[Omnimon] in name [When Digivolving] <De-Digivolve 3> 1 of your opponent's Digimon. Then, choose any number of your opponent's Digimon so that their play cost total is up to 6 and delete them. [When Attacking] By trashing up to 3 level 6 or higher cards in this Digimon's digivolution cards, among your opponent's Digimon and Tamers, delete 1 with the lowest play cost for each card trashed. If you trashed 3 cards, trash the top 2 cards of your opponent's security stack.
Lv.7 Omnimon Alter-B EX4-073 SEC Mega | Virus | Holy Warrior Digivolve: 2 from Lv.7 w/[Omnimon] in name [When Digivolving] <De-Digivolve 3> 1 of your opponent's Digimon. Then, choose any number of your opponent's Digimon so that their play cost total is up to 6 and delete them. [When Attacking] By trashing up to 3 level 6 or higher cards in this Digimon's digivolution cards, among your opponent's Digimon and Tamers, delete 1 with the lowest play cost for each card trashed. If you trashed 3 cards, trash the top 2 cards of your opponent's security stack.
Lv.7 Omnimon Alter-B EX4-073 SEC
Mega | Virus | Holy Warrior
{{DigivolveFromArchetypes|2|7|Omnimon}}
[When Digivolving] <De-Digivolve 3> 1 of your opponent's Digimon. Then, choose any number of your opponent's Digimon so that their play cost total is up to 6 and delete them.
[When Attacking] By trashing up to 3 level 6 or higher cards in this Digimon's digivolution cards, delete 1 of your opponent's Digimon or Tamers with the lowest play cost for each card trashed. If you trashed 3 cards, trash the top 2 cards of your opponent's security stack.Lv.7 オメガモン Alter-B EX4-073 SEC 究極体 | ウィルス種 | 聖騎士型 【進化時】相手のデジモン1体を≪退化3≫。その後、登場コスト合計6まで相手のデジモンを選び、選んだデジモン全てを消滅させる。 【アタック時】このデジモンの進化元から、Lv.6以上のカード3枚までを破棄することで、破棄したカード1枚ごとに、相手のデジモンとテイマーの中で最も登場コストの低い1体を消滅させる。3枚破棄したなら、相手のセキュリティを上から2枚破棄する。