7 official rulings from Bandai, last ruled Mar 28, 2024. Straight answers to how this card actually resolves.

After using this card, I digivolve a red Digimon into a white Digimon card. What color card can I trash from my hand to reduce the memory cost of the digivolution?
You can trash a red Digimon card to reduce the digivolution cost. The card you can trash with this effect must match the color of the Digimon performing the digivolution in your battle area.
Ruled Mar 28, 2024
I’m digivolving a Digimon in my breeding area. Can I reduce the digivolution cost by 4 with this card's effect?
No, this effect can't reduce digivolution costs of Digimon in breeding areas.
Ruled Mar 28, 2024
During the turn I use this card, if I have a blue Digimon in my battle area with an effect that reads, “This Digimon is also treated as red,” can I trash a red Digimon card in my hand to reduce the digivolution cost by 4?
Yes, you can.
Ruled Mar 28, 2024
After using this card, I activate [BT7-085]/[Takuya Kanbara]’s <Main Timing> effect. Can I use this card's effect specifically to trash cards with [Hybrid] in their traits from my hand, so that I can place them under [Takuya Kanbara] using its effect?
No, you can't. You don't trash the card in your hand with this effect until you digivolve. [BT7-085]/[Takuya Kanbara]’s <Main Timing> effect reads, “You may place 5 cards with [Hybrid] in their traits from your trash under this Tamer in any order,” and is used to digivolve into [EmperorGreymon]. As such, you place the cards under [Takuya Kanbara] before you begin digivolving, at which point you can trash a card in your hand with this card's effect.
Ruled Mar 28, 2024
When digivolving from a multicolor Digimon, what color cards can I trash with this card’s effect to reduce the digivolution cost?
The card you trash can match any one of the Digimon’s colors. For example, when digivolving a blue/green Digimon, you can trash either a blue or a green card.
Ruled Mar 28, 2024
Can I reduce the memory cost of a DNA digivolution with this card's effect? If I can, what color cards can I trash with this card’s effect?
Yes, you can. The card you trash can match any of the colors of either Digimon. For example, when DNA digivolving a blue Digimon and green Digimon, you can trash either a blue or green card.
Ruled Mar 28, 2024
After using this card, can I reduce the digivolution cost of my digivolving Digimon by trashing 1 Digimon card in the hand with the same color when an effect to digivolve one of my Digimon is activated?
Yes, you can.
Ruled Mar 28, 2024
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Questions and answers are Bandai's official rulings, collected and translated by the DigimonCardGame Wiki community and reused here under CC BY-SA. Card names and card text are © their respective publishers; Combalo is not affiliated with Bandai.