Rulings
Q1: Is "Digivolve While you have 2 or fewer security cards, Agumon: Cost 3" a digivolution requirement added by an effect while I have 2 or fewer security cards?
No, this is a standard digivolution requirement for a Digimon card. It references the number of your security cards, but it's not an effect.
Q2: Can I use Blast Digivolve to digivolve my Agumon into this card in the hand when I have 2 or fewer security cards and an opponent's Digimon attacks?
Yes, you can. Digivolution is possible as long as you have 2 or fewer security cards when you use Blast Digivolve.
Q3: If an opponent's Digimon attacks when I have 2 or fewer security cards, then an effect adds a card to my security stack so my security stack has 3 or more cards when I use Blast Digivolve, can my Agumon digivolve into this card in the hand?
No, it can't. Digivolution from Agumon isn't possible because the digivolution requirements aren't met when you use Blast Digivolve.
Q4: If an opponent's Digimon attacks when I have 3 security cards, then an effect removes a card from my security stack so my security stack has 2 or fewer cards when I use Blast Digivolve, can my Agumon digivolve into this card in the hand?
Yes, it can. Digivolution from Agumon is possible as long as the digivolution requirements are met when you use Blast Digivolve.
Q5: If I use an effect such as P-103 Offense Training's Delay that digivolves a Digimon, can my Agumon digivolve into this card in the hand when I have 2 or fewer security cards?
Yes, it can.
Q6: What does "On Play When Digivolving Delete your opponent's Digimon up to a total DP equal to this Digimon's DP" mean, exactly?
This effect allows you to choose any number of your opponent's Digimon whose total DP adds up to the same as this Digimon's DP or less, then you delete all of them. For example, if this Digimon has 14000 DP when its On Play When Digivolving effect activates, you can choose any number of your opponent's Digimon whose DP adds up to a total of 14000 or less, such as 1 with 10000 DP and 1 with 4000 DP, or 2 of their Digimon with 7000 DP each, then you delete them.
Q7: Can I intentionally choose targets whose total DP adds up to a lower value than this Digimon's DP?
Yes, you can choose any targets as long as their total DP adds up to a value less than or equal to this Digimon's DP. However, you must choose at least 1 of your opponent's Digimon whose total DP is equal to or less than this Digimon's DP.
Data Sources
Lv.7 Agumon - Bond of Bravery ACE LM-021 P Mega | Unknown | Unknown [Digivolve] While you have 2 or fewer security cards, [Agumon]: Cost 3 [Hand] [Counter] <Blast Digivolve> (Your Digimon may digivolve into this card without paying the cost.) [On Play] [When Digivolving] Delete up to this Digimon's DP's total worth of your opponent's Digimon. [When Attacking] [Once Per Turn] If you have a Tamer, trash your opponent's top security card. --- Inherited: <Overflow (-5)> (As this card moves from the field or under a card to an area other than those, lose 5 memory.)
Lv.7 Agumon - Bond of Bravery ACE LM-021 P Mega | Unknown | Unknown [Digivolve] While you have 2 or fewer security cards, [Agumon]: Cost 3 [Hand] [Counter] <Blast Digivolve> (One of your Digimon may digivolve into this card without paying the cost.) [On Play] [When Digivolving] Delete your opponent's Digimon up to a total DP equal to this Digimon's DP. [When Attacking] [Once Per Turn] If you have a Tamer, trash the top card of your opponent's security stack. --- Inherited: <Overflow (-5)> (When this card would move from the battle area or under a card to another area, lose 5 memory.)
Lv.7 Agumon - Bond of Bravery ACE LM-021 P Mega | Unknown | Unknown [Digivolve] While you have 2 or fewer security cards, [Agumon]: Cost 3 [Hand] [Counter] <Blast Digivolve> (One of your Digimon may digivolve into this card without paying the cost.) [On Play] [When Digivolving] Delete any number of your opponent's Digimon whose total DP adds up to equal or less than this Digimon's DP. [When Attacking] [Once Per Turn] If you have a Tamer, trash the top card of your opponent's security stack. --- Inherited: <Overflow (-5)> (As this card moves from the battle area or under a card to another area, lose 5 memory.)
Lv.7 アグモン -勇気の絆-ACE LM-021 P 究極体 | 不明 | 不明 自分のセキュリティが2枚以下の間、「アグモン」:コスト3 ［手札］【カウンター】≪ブラスト進化≫（自分のデジモンをこのカードにコストを支払わずに進化できる） 【登場時】【進化時】DP合計このデジモンのDPまで、相手のデジモンを消滅させる。 【アタック時】[ターンに1回]自分のテイマーがいるなら、相手のセキュリティを上から1枚破棄する。 --- Inherited: ≪オーバーフロー《-5》≫（バトルエリアかカードの下から、それ以外の場所に送られる場合、メモリー-5）