Rulings
Q1: What does Trash in this card's End of Your Turn effect mean?
It means that the effect will activate at the specified timing if this card is in your trash.
Q2: After deleting 1 of my Digimon with digivolution cards and {{EffectLinkArchetype|Gallantmon}}, can I choose to not play this card for this card's End of Your Turn effect?
Yes, the effect reads “you may play," so you can choose not to play it.
Q3: Does "For every 10 total cards in both players' trashes" in this card's On Play effect mean every 10 cards in either me or my opponent's trashes?
No, it means every 10 cards in the total sum of cards in your trash and the cards in your opponent's trash. For example, if you have 15 cards in your trash and your opponent has 9 cards in their trash, the total would be 24. Therefore, you add 4000 to the maximum this DP-based deletion effect can delete, and you can now delete 1 of your opponent's Digimon with 11000 DP or less.
Data Sources
Lv.6 ChaosGallantmon EX4-011 R Mega | Virus | Dark Knight [Trash] [End of Your Turn] By deleting 1 of your Digimon with digivolution cards and [Gallantmon] in its name, you may play this card without paying the cost. [On Play] Delete 1 of your opponent's Digimon with 7000 DP or less. For every 10 total cards in both players' trashes, add 2000 to the maximum this DP-based deletion effect can delete.
Lv.6 ChaosGallantmon EX4-011 R Mega | Virus | Dark Knight Digivolve: 3 from Lv.5 w/[WarGrowlmon] in name [Trash] [End of Your Turn] By deleting 1 of your Digimon with digivolution cards and [Gallantmon] in its name, you may play this card without paying the cost. [On Play] Delete 1 of your opponent's Digimon with 7000 DP or less. For every 10 total cards in both players' trashes, add 2000 to the maximum this DP-based deletion effect can delete.
Lv.6 ChaosGallantmon EX4-011 R
Mega | Virus | Dark Knight
{{DigivolveFromArchetypes|3|5|WarGrowlmon}}
[Trash] [End of Your Turn] By Deleting 1 of your Digimon with a digivolution card and [Gallantmon] in its name, you may play this card without paying its cost.
[On Play] Delete 1 of your opponent's Digimon with 7000 DP or less. For every 10 total cards in both player's trashes, add 2000 to the maximum DP you can choose with DP-based deletion effects.Lv.6 カオスデュークモン EX4-011 R 究極体 | ウィルス種 | 暗黒騎士型 ［トラッシュ］【自分のターン終了時】進化元を持つ名称に「デュークモン」を含む自分のデジモン1体を消滅させることで、このカードをコストを支払わずに登場できる。 【登場時】DP7000以下の相手のデジモン1体を消滅させる。お互いのトラッシュ合計10枚ごとに、このDP消滅効果の上限+2000。