The hand seals for releasing Impure World Reincarnation were, in order: Rat, Ox, Monkey, Tiger, Dragon, Boar.
Of course, Wu Yu did not remember them because he had read the manga.
Who would go out of their way to memorize that stuff?
Back when he first created Right Mysterious Orochimaru and asked him to compile the Orochimaru Scroll, Wu Yu had wanted to prevent him from exercising any "initiative"—
Things like Orochimaru's Wind Release, Earth Release, and snake-style claw techniques were either things Wu Yu already had plenty of or things he had no interest in adding to his ninjutsu repertoire. If Right Mysterious Orochimaru left those out of the Orochimaru Scroll, he couldn't give a damn.
But Wu Yu had paid particular attention to techniques involving the Cursed Seal and Impure World Reincarnation, explicitly insisting that Right Mysterious Orochimaru record them.
Naturally, those included the seals for releasing Impure World Reincarnation.
However—
Just as Wu Yu used Lesser Formless Sage Art: Sharingan Hypnosis on Orochimaru and ordered him to release the reincarnations before them, several Chakra Chains shot toward Wu Yu as the dazed Orochimaru slowly formed the fourth seal, Tiger.
The Chakra Chains possessed powerful sealing and restraining properties, and their sharp tips pierced the chakra layer of the enormous Immortal Beast Jade Rabbit enveloping Wu Yu. At the same time, the temperature on the other side suddenly soared, and a crimson Great Fireball roared toward him.
"..."
Wu Yu caught the Chakra Chains that had pierced his Jade Rabbit Immortal Beast form in one hand and yanked the reincarnated Kushina Uzumaki toward him. At the same time, he raised his other hand toward the Great Fireball spat out by the reincarnated Fugaku Uchiha. The Golden Steel Ring flew from his wrist, and the blazing, enormous fireball surged