Q1: This card has Agumon in its name, but is it also treated as a Digimon card or a Digimon?

No, it isn't. It will only be treated as a Digimon if an effect treats it as a Digimon.

Q2: What does an "is also treated as a Digimon with X000 DP" effect do, exactly?

It causes that card to also be treated as a Digimon with X000 DP. For example, if a Tamer is also treated as a Digimon, it can attack like a standard Digimon, and it will gain inherited effects from cards stacked under it. However, even if a Tamer is played and then treated as a Digimon in the same turn, it can't attack during that turn.

Q3: If a Tamer is also treated as a Digimon using an "is also treated as a Digimon with X000 DP" effect, is it no longer considered a Tamer?

No, it is treated as both a Digimon and a Tamer.

Q4: If a Tamer is also treated as a Digimon using an "is also treated as a Digimon with X000 DP" effect and it activates an effect, is it treated as both a Digimon effect and a Tamer effect?

Yes, it's treated as an effect of both. Because the card is treated as both a Digimon and a Tamer, the activated effect is treated as both a Digimon effect and a Tamer effect.

Q5: If a Tamer is also treated as a Digimon using an "is also treated as a Digimon with X000 DP" effect, then another effect causes its DP to become 0, is it deleted upon a rule check?

Yes, it's deleted upon the rule check timing.

Q6: If a Tamer is also treated as a Digimon using an "is also treated as a Digimon with X000 DP" effect, and later it gains another "is also treated as a Digimon with X000 DP" effect, what happens?

If an effect has triggered and the card is affected by a "is also treated as a Digimon with X000 DP" effect, the play cost, level, and DP are overwritten by the newer effect. However, if an effect has already activated and the card is affected by a "is also treated as a Digimon with X000 DP" effect, the already activated effect will be overwritten. Any other effects such as Rush that are later gained will be added.

Q7: Can I gain memory using an effect on a Tamer that's treated as a Digimon with X000 DP due to an effect while my opponent has "your opponent can't gain memory other than by Tamer effects" activated?

Yes, you can. When an effect is activated on a card that's treated as both a Digimon and a Tamer, the effect is treated as both a Digimon effect and a Tamer effect, therefore you can gain memory.

Q8: If an opponent's card has "isn't affected by Digimon effects" and it's chosen for an "is also treated as a Digimon with X000 DP" Tamer effect that treats it as a Digimon, will the chosen opponent Digimon be affected by effects?

No, it won't be affected by effects. When an effect is activated on a card that's treated as both a Digimon and a Tamer, the effect is treated as both a Digimon effect and a Tamer effect, therefore the chosen opponent Digimon won't be affected by effects.

Q9: I have this card and 1 Marcus Damon in the battle area. I place BT21-044 RizeGreymon in the battle area by playing or digivolving, and the memory moved to 1 or more on my opponent's side. Can I use BT21-044 RizeGreymon's On Play When Digivolving effect to have 1 of my Digimon attack, resolve the attack, then use this card's End of Your Turn effect to have 1 of my Digimon attack?

Yes, you can. Even if you pay a cost and the memory moves to 1 or more on the opponent's side during the main phase, first any effects that triggered during that timing must resolve, then the end of the turn timing occurs. In this case, once all of the attacks from RizeGreymon's On Play When Digivolving effect have resolved, then the end of the turn timing will occur. Because the attack has already resolved and isn't currently occurring, you can activate this card's End of Your Turn effect and have 1 of your Digimon attack.

Q10: I have 2 copies of this card in the battle area. At the end of my turn, I used the End of Your Turn effect on the 1st copy of this card to attack. Can I then use the End of Your Turn effect on the 2nd copy of this card to attack?

No, an attack using the 2nd effect isn't possible. A new attack declaration can't be made during an attack. In this case, the End of Your Turn effects on both copies of this card trigger simultaneously at the end of your turn, and you use the End of Your Turn effect on the 1st copy of this card to attack. The 2nd End of Your Turn effect can be activated before the counter timing, but because you can't declare another attack during an attack, you won't be able to attack using the 2nd effect, even if you activate it.

Q11: I have this card and a yellow Digimon with Agumon or Greymon in its name in the battle area. At the end of my turn, can I choose to not activate this card's End of Your Turn effect?

No, you can't. If your turn ends while you have a yellow Digimon with Agumon or Greymon in its name in the battle area, you must choose 1 of your Marcus Damons, and it will gain the "is also treated as a 6000 DP Digimon, gains Rush, and can't digivolve" effect. Then, you choose whether or not 1 of your Digimon will attack using the part of the effect after "then." At such times, Once Per Turn is considered to be used, even if you don't have 1 of your Digimon attack using the part of the effect after "then."