When The Batman Who Laughs used the head Chen Tao had once chopped off to complete his resurrection through another body, he had already completely freed himself from Mandrakk's influence without letting Mandrakk notice.
If he had to put it bluntly, Chen Tao believed all of this had been part of The Batman Who Laughs's plan. At the very least, he had escaped perfectly. The body polluted by Celestial Blood had now become a remotely controlled puppet of The Batman Who Laughs, while Mandrakk had completely lost the means to threaten him.
But interestingly, The Batman Who Laughs had retained control over that polluted body.
This meant that even if Chen Tao controlled his current body, should Chen Tao try to impose conditions he found completely unacceptable...
He could abandon this unpolluted body, transfer his main consciousness back into the body of Mandrakk's The Batman Who Laughs, and then seek another way to escape his control.
Thus, although it seemed that Chen Tao controlled his entire body, he had not completely lost his autonomy. In fact, he had been born invincible--
If he was willing to abandon this unpolluted body, Chen Tao had nothing with which to threaten him.
So Chen Tao first proposed his bottom-line condition:
"You'd better hand over Prime Universe Barry Allen, The Flash, along with the other half of Cyborg."
The members of the Prime Universe Justice League had to be saved.
This was not merely a matter of heroic duty. It was also because the completeness of the Prime Universe Justice League concerned the most basic immune system of the entire DC Multiverse.
"That's completely doable, my friend."
The Batman Who Laughs merely snapped his fingers twice. The next moment, a pink Thunder Sprite appeared in front of Chen Tao.
This Fifth Dimension creature snapped