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

After using this Digimon's effect to digivolve it into [AncientGreymon], I digivolve (or de-digivolve) it into another Digimon. Do I still have to delete it at the end of the turn?
Digimon carry over effects after digivolving or de-digivolving, so you still have to delete this Digimon at the end of the turn.
Ruled Mar 28, 2024
After using this Digimon's effect to digivolve it into [AncientGreymon], I use [BT5-109]/[Mega Digimon Fusion!] to digivolve it into a level 7 Digimon. At the end of the turn, which effect takes precedence: This card's "delete this Digimon at the end of the turn" effect, or [Mega Digimon Fusion!]'s "return the Digimon that digivolved with this effect to the bottom of its owner's deck" effect?
They both trigger at the same time, so you can choose which order to activate them in. The one you activate first takes precedence.
Ruled Mar 28, 2024
After using [BT3-109]/[Back for Revenge!] on this Digimon, I use this Digimon's effect to digivolve it into [AncientGreymon]. When this Digimon is deleted at the end of the turn, which Digimon does [Back for Revenge!]'s effect allow me to re-play to my battle area? This card, or [AncientGreymon]?
Digimon carry over effects after digivolving, so [AncientGreymon] is the Digimon re-played in your battle area.
Ruled Mar 28, 2024
Got a line that uses Agunimon? Map it in the builder and share it with a link.
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.