9 official rulings from Bandai, last ruled Nov 1, 2024. Straight answers to how this card actually resolves.

Can the play cost of a Digimon with the [Royal Knight] be reduced due to the <Your Turn> effect of my opponent's [BT13-007]/[King Drasil_7D6] if [BT8-071]/[Psychemon] is in play?
No, they can't be reduced. [BT8-071]/[Psychemon]'s effect does not target Digimon, so even if your opponent's [BT13-007]/[King Drasil_7D6] is in the breeding area, its effect to reduce play costs can't be activated.
Ruled Mar 28, 2024
When I use this card's <Start Your Main> effect to place a BT17-078 [Omnimon ACE] under this card as a digivolution card, is BT17-078 [Omnimon ACE] processed?
No, it isn't processed. <Overflow> is processed when a card is sent from the area or from under a card to another area. In this case, <Overflow> isn't processed because a card from the area is placed under another card.
Ruled Sep 13, 2024
Does this card's 1st [Breeding] <Your Turn> effect allow my Tamers to digivolve using digivolution requirements for digivolving from Tamers?
Yes, they can be digivolved.
Ruled Nov 1, 2024
What does "further reduce it by 1 for each of this Digimon's digivolution cards" in this card's 2nd [Breeding] <Your Turn> effect mean, exactly?
This effect additionally increases the numerical value of the play cost reduction in "when a [Royal Knight] Digimon card would be played, you may reduce the play cost by 4" in this carad's 2nd [Breeding] <Your Turn> effect. For example, if this Digimon has 1 digivolution card, the numerical value of the play cost reduction will be 5.
Ruled Nov 1, 2024
Can I choose to not reveal the top card of my Digi-Egg deck and not place my [Royal Knight] Digimon as this Digimon's bottom digivolution cards for this card's [Breeding] <Start Your Main>?
No, you must perform as much of the processing as possible.
Ruled Nov 1, 2024
If multiple cards are placed as the bottom digivolution cards for this card's <Start Your Main> effect, what order are the cards placed?
The player that activated the effect chooses the order of the bottom digivolution cards that are placed. Note that the cards placed by this effect must be placed under any already placed digivolution cards.
Ruled Nov 1, 2024
Does this card's [Breeding] <Your Turn> effect also prevent my Digimon from DNA digivolving or burst digivolving?
That's correct, such digivolutions are also not possible.
Ruled Nov 1, 2024
Does this card's 1st [Breeding] <Your Turn> effect allow my Tamers to digivolve using a "you may digivolve as if your Tamer is a level 3 Digimon" effect?
No, they can't be digivolved.
Ruled Nov 1, 2024
Does using [BT10-110]/[Seiken Meppa] trigger this card's inherited effect to gain memory?
No, using and activating [BT10-110]/[Seiken Meppa]'s <Main Timing> effect does not cause a card to be "placed" in the Battle Area, so this card's inherited effect does not trigger.
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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.