Jumba had designed the perfect experiment, 626 aka "Stitch". Incredible durability, immense strength, a supercomputer-like brain, among other things. It was time to claim that body and make it his! Pouring a potion on Stitch, it gave the little blue fluffball a toon-ish ability to stretch. Jumba immediately got to work, scooping Stitch up and slipping his fat legs in. Inch by inch he tugged Stitch over his hefty frame and finally slid himself all the way in.
Stitch laid dazed and confused as his massive Jumba-sized gut wriggled and squirmed. He felt something odd; thick arms and legs sliding into his own, stretching them out as the limbs of his creator soon nestled into place. Stitch's bigger fingers and toes would now slowly wiggle of their own accord. Next, Stitch felt the massive bulge that was Jumba's head now moving up. There was a bit of tightness going into Stitch's head for Jumba due to 626's smaller size but eventually with enough pushing, his head slotted into place and the black eyes of Experiment 626 closed.
Moments passed and a much thicker and taller 'Stitch' sat up, his eyes opened up to reveal Jumba's yellow coloration as he smirked with glee. This powerful (and fluffy!) body was his now. Jumba stood up to admire his new blue form, running his hands over his still chubby belly and combing his new claws through his fur. Those yellow, evil genius eyes glanced over to a spare pair of his casual wear and he sauntered on over. Tugging his shorts up over his thighs he chuckled at the feeling of the material rubbing over HIS blue fur. With a tug of the waistband and a release it snapped into place on his hips. Next, he picked up his Hawaiian shirt and slid both arms up into the sleeves, quickly buttoning it up and now reclining back to admire the look of his stolen form; evil genius brain and genetic experiment brawn.. one perfect package of creator and created~

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A wonderful comic done by  BembosDoggo seriously go watch them!

Jumba Jookiba & Stitch © Disney