Since this monster can be easily Special Summoned to the Field to make a direct attack in order to bypass your monsters defense, using Drowning Mirror Force will return it to the Extra Deck, however you opponent can chain with another Mask Change to halt Masked HERO Anki’s direct attack and send it to the Graveyard, since the ruling is that, when a monster that declared an attack is sent to the Graveyard, then it is no longer treated as a monster that declared an attack.
Returns from your opponent's field to your opponent's Deck
My Masked HERO Anki declared a direct attack and my opponent used Drowning Mirror Force, I chained with a mask change, get another Masked HERO Anki on the field and it was returned to the deck when the chain resolved.
Maybe because you lose ALL attack monsters? Shuffling back into the deck is for most decks no real help. It's a hardcore stall card. There is nothing tactical to use except to prepare a own OTK with such cancer cards.