Arcana Force 0 - The Fool, in the animation, was originally a card that Saiou sneakily inserted into Judai's deck before the duel began and then forcibly special summoned it to Judai's field during the duel.
The Fool that appeared on Judai's field in the animation was in reverse position. The effect of this card in the reverse position is that it does not accept any magic trap monster effects from its controller—it cannot be targeted nor affected by effects.
Moreover, this card cannot be destroyed by battle, and when summoned in attack position, it cannot actively change to defense position.
So at that time, this thing was just a live target on Judai's field, with an attack power of 0 and unable to turn to defense. Even if one wanted to use card effects to get rid of it, it wouldn't accept any of its controller's card effects. It was truly a professional traitor, living up to the name "The Fool."
But if it were in the upright position, its effect would change to "cannot be targeted or affected by opponent's effects," and coupled with resistance to battle destruction, it's almost an invincible shield.
...Of course, it's only almost.
It ultimately became fodder for the invincible turtle.
Suddenly, a large and clumsy blue turtle erupted from Saiou's field, its massive claws unceremoniously grabbing The Fool and tossing it into its mouth, crunching away contentedly.
When finished, the turtle stood contentedly on Saiou's field.
[Sea Turtle Kaiju - Gameciel, Attack Power 2200]
Saiou wanted to curse.
Darn, what kind of crap is this?
I don't want this big oaf, get it off my field!
Then Judai continued: "Next, I'll activate the effect of 'Elemental Hero Grand Neos!' Once per turn, it can return one monster on the opponent's field to the owner's hand!"
Having been inwardly furious about the turtle, Saiou was suddenly taken aback.
This effect... Could it be!?
"That's right," Judai beamed with a bright smile, "I'm going to return 'Sea Turtle Kaiju - Gameciel' to the hand! And since the original owner of 'Sea Turtle Kaiju - Gameciel' is me, of course, it's going back to my hand!"
Grand Neos raised its arm, the drill spinning. The drill in its hand pierced through the air, creating a nebula-like hole behind the Sea Turtle Kaiju, and the terrifying force unceremoniously sucked it in!
Nebula Hole!
The turtle transformed into a golden beam of light and flew back to Judai's hand.
Saiou realized how serious the situation was.
You use Sea Turtle Kaiju to devour my monster... and then the Sea Turtle Kaiju can be retrieved?
Yikes, doesn't this mean that stinking turtle can eat my monster next turn!?
Gasp—
Finally realizing how fiendish this strategy was, Saiou inhaled sharply.
Yet, that's not even the most fiendish part.
If you pair the mole with Sea Turtle Kaiju, you can achieve an infinite loop—having the turtle eat the opponent's monster, then summon the mole to attack the turtle, bouncing both the mole and turtle back to the hand. In the next turn, the turtle can eat the opponent's monster again, then summon the mole to bounce both back to the hand...
Even Judai, used to his usual solitary style, couldn't help but marvel at how perfect the pairing of these two cards was!
No wonder Teacher Youyu put this turtle in my deck, saying it suited me... Looking at it this way, Teacher Youyu really knew everything!
He even felt that this card, 'Sea Turtle Kaiju - Gameciel,' was practically tailored for his mole!
These two are undoubtedly a pair of fiendish golden partners!
"I haven't performed a normal summon this turn," Judai said, "I summon 'Elemental Hero Neos Alius' in attack position!"
A flash of white light, and the petite Neos Alius jumped onto the field.
[Elemental Hero Neos Alius, Attack Power 1900]
"Battle!" Judai announced, "Elemental Hero Grand Neos, direct attack!"
Grand Neos' drill transforms into a blurred, spinning semblance, energy continuously surging from its body and clinging to the drill, the spiraling beam piercing through the air!
But of course, Saiou wasn't one to be underestimated: "Then I activate a Set Card! Trap Card 'Nitwit Outwit!' Discard a Monster Card from my hand, and select a monster on the field!
The selected monster's attack power is reduced by the original attack power of the discarded monster!"
He revealed a card in his hand.
"I discard 'Arcana Force XVIII - The Moon' from my hand, reducing Grand Neos' attack power by 'The Moon's' attack power—2800 points!"
"The Moon" appeared in spectral form before Saiou, and the spiraling beam fiercely struck the body of the Arcana Force, but it was not successfully penetrated, being negated instead.
[Elemental Hero Grand Neos, Attack Power 2500 → Attack Power 0]
"Then 'Elemental Hero Neos Alius,' direct attack!"
Neos Alius lunged forward to make a quick attack, but seemingly still within Saiou's calculations.
"Discard 'Arcana Force XIV - Temperance' from my hand, setting battle damage to zero!" Saiou sneered, "Nada!"
The translucent phantom of Temperance appeared, stopping Neos Alius's charge.
"They've all been blocked... Your duel isn't all that bad, after all!"
Saiou's forehead veins bulged.
What do you mean it's not all that bad? What made you think I'm not doing well?
"I'll set two cards face-down and end my turn," Judai said, "The active time for 'Elemental Hero Grand Neos' is only one turn, and during the end phase, it must return to the deck."
Grand Neos soared up with a shout, disappearing beyond the heavens without a trace.
"Neos Alius only has one turn of active time?" Saiou frowned.
Originally, he thought keeping Grand Neos with 0 attack power on the field would be a breakthrough point, but he didn't expect Neos Alius to leave the field automatically. Neos Alius's "only existing for one turn" side effect turned out to be beneficial.
"It's my turn, draw a card." Saiou swung his hand, "Activate the Set Card! Trap Card 'Sixth Sense!' Declare two numbers between 1 and 6, and the opponent rolls a die!
If one of the declared numbers is rolled, I can draw that number of cards from the deck!
But if none of the declared numbers is rolled, I must send that number of cards from the top of my deck to the graveyard."
"Another luck-based card?" Judai eagerly prepared, "When it comes to luck, I'm quite confident!"
"Luck? Ha-ha-ha, such a thing is needed only by mere mortals, but not by me!" Saiou arrogantly said, "The numbers I declare are five and six!"
"Wow, starting with the biggest numbers?"
Judai took a deep breath.
"Alright! Then I'll roll!"
The giant die fell from the air, spinning a few rounds, stopping in the middle of the Dueling Arena.
A big "6."
"Huh? Is it really a 6?" Judai was surprised.
"Ha-ha-ha, I told you, destiny is predetermined!" Saiou boasted with delight, "According to 'Sixth Sense's' effect, I draw six cards from my deck!
The symphony of fate is about to reach its finale, Yuki Judai, and this will be your destiny's last turn!"