This card basically stops the opponent from using an effect that searches a card out from the deck, and considering how universal those kinds of effects are to good deck building, it's no surprise Ash is as popular as it is
Adventure cards are treated as if they are only the creature half at all times except when they are on the stack being cast as the adventure.
High Tide Gyojin
The Reaver Cleaver and Sword of Feast and Famine generate mana and value with each swing, while Conqueror's Flail and Champion's Helm protect your threats and disrupt opponents
Furthermore, if it is destroyed, D can be revived, and it can also be revived itself, so it becomes a perpetual machine of Friche removal, and it is somewhat strong against removal other than destruction, where this kind of card is weak
MTG introduced a new type of card in 2021 going into Zendikar Rising Standard: modal double-faced cards or MDFCs