Effect
During the End Phase, if this card is in the Graveyard because it was sent there by an opponent's card effect this turn while in your possession: You can add, from your Deck to your hand, 1 monster with a different Level from the monsters you control and the monsters in your Graveyard. You can only use this effect of "Dogu" once per turn.
The monster effect "①: During the End Phase of the turn this card was sent to the GY by an opponent's effect: You can add 1 monster from your Deck to your hand whose Level is not present on your field or in your GY" is a Trigger Effect that activates in the GY. (It does not target. You choose a monster from your Deck whose Level is not present on your field or in your GY when resolving the effect.)
If all monsters in your Deck have the same Level as at least one monster present on your field or in your GY, there is no monster you can add to your hand, and therefore you cannot activate the effect.
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