You can only control 1 "Dakki, the Graceful Mayakashi". When a "Mayakashi" monster(s) is Special Summoned to your field from the Extra Deck, while this card is in the GY (except during the Damage Step): You can Special Summon this card. You cannot Special Summon monsters from the Extra Deck the turn you activate this effect, except "Mayakashi" monsters.
Self revival relies on Special Summoning Mayakashi from the Extra deck.
Dakki is essential to the Mayakashi synchro climb. Synchro Summon any Mayakashi and revive Dakki to make the next level of Mayakashi monster. This combo can bring you from the level-3 Oboro-Guruma to the level-9 Yoko in a single turn while also setting up your graveyard.
Shafu can revive a Dakki in your graveyard to make Tsuchigumo. This can be helpful when your synchro climb is disrupted by your opponent removing Dakki, or when you search Dakki by pitching her to the graveyard.
Searching Dakki with Mayakashi Return lets you get to your synchro plays more consistently. Effects that pitch Dakki to the graveyard, such as Yuki Musume and Gozuki, can be just as effective because of her self revival effect. Lastly, she can be Special Summoned from the deck by Shiranui Solitaire which is one of the ways Mayakashi can synergize with Shiranui.