Gonna try doing each final stage Pokemon with Krystal in their stomach, unless a lower stage evolution could possibly eat her (like Onix and Steelix, etc). Although, if a final stage Pokemon is too small to possibly eat her, it still will. Same with single stage evolution Pokemon being too small. They will just have an overly bloated belly and poor Krystal will be VERY cramped. These will be AUs as if the characters from "Test Food" were in the Pokemon universe.
I will also make a short story with each. Enjoy >:)

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Walking through the forest, Krystal spotted something bright pink in the distance. As she rounded a corner, she found the large spotted petals atop a base that almost looked like a small tree trunk. This was all carried on the back of a light blue, bumpy Pokemon. Krystal had never seen a Venusaur up close before so all she could do was stand there and stare. The Venusaur then turned around, now facing her direction with droopy scarlet eyes.
As it spotted her, Krystal froze momentarily. She had heard that Venusaur weren't necessarily aggressive Pokemon but the sheer size of it made her a bit uneasy.
"Saur," it greeted.
'Maybe I'm just overreacting.' Krystal thought. The Venusaur looked friendly enough after all, or at least unthreatening with its bored expression. Pushing her anxious thoughts aside, she stepped into the clearing, coming closer to the Pokemon.
"Hey there Venusaur," she said.
It watched her as she made her way toward it, maintaining the same expression. Suddenly, its eyes narrowed and mouth curved into a smirk. Before Krystal could react, two massive vines shot out from under Venusaur's leaves and wrapped around her torso. She yelped as she was yanked off of the ground and hung in the air over Venusaur's head. It stared up at her, smirking deviously.
Krystal's anxiety flared up again. "Wh-what are you doing Venusaur?"
Venusaur swiped its tongue over its lips. Krystal's heart skipped a beat and her face heated up. Venusaur aren't carnivores, are they?? Maybe it just wanted a taste. But the way it was looking at her felt much more sinister than that.
Its vines pulled her down to be level with its face, staring at her the whole time. Slowly and deliberately, it opened its huge mouth, saliva stringing from its fangs. Now that she thought about it, why would a Venusaur have sharp teeth if it were an herbivore?
"No, please don't do this!" she pleaded.
Ignoring her pleas, it pushed her into its waiting maw head-first. Her hands flew up to its upper lip, clinging to the outside in an attempt to prevent herself from going in.
"No no no! Caleb, someone, help!" She screamed. She never should have gone off on her own. Her Pokemon were camping out with Caleb and his Pokemon, eating dinner. Hopefully someone would hear her cries and come to her rescue before she became dinner herself.
The attempts to hold on to the outside of its mouth proved futile as its powerful vines just needed to tug a little bit harder to dislodge her hands. Once the vines carried her deeper into Venusaur's mouth, they released her and withdrew outside. Krystal plopped onto the slimy tongue, spinning around just as Venusaur's mouth clamped shut.
"Venusaur..." it purred through a mostly closed mouth, its hot breath buffeting her as it rose from its throat. Its tongue curled up to wrap around her, soaking and blanketing her body with the large muscle.
Krystal's face flushed a deep red color. No matter how terrified she was for her life, she couldn't deny how good it felt to be wrapped in such tight warmth. Being massaged by its wet tongue and desired as even just a meal sent a thrill through her whole body. She didn't have a death wish by any means but it wasn't like she had a choice in the matter.
After Venusaur had taken enough time teasing and tasting its prey, its tongue pushed her to the back of its mouth. Fear and urgency returned to Krystal as she was faced with the dark, gaping throat in front of her. Falling back on her butt, she tried to turn away from its throat in an attempt to get away. But to no avail. All it took was a single gulp to suck her in. She ended up head-first again, being pulled in deeper by flesh flanking her on all sides. Her arms were pinned to her sides, preventing even the thought of escape.
Not a single shred of light could be seen now so the rest of Krystal's senses were at an all-time high. The rancid smell of its insides. The awful taste of mucus forced in her mouth. Contrastingly, the wonderful feeling of powerful yet soft flesh tugging her body deeper and deeper inside. Finally, the thrilling yet terrifying sound of growling getting louder and louder as she was unwillingly pushed to her final destination.
After a short journey, Krystal felt her head push against a sturdy yet soft wall. The growling sound now surrounded her with nearly ear-shattering intensity. She didn't need anyone to tell her that she had reached Venusaur's stomach. As the rest of her body was shoved in, she found herself automatically curling into the fetal position. The air grew thinner and hotter as her feet fell into place with the rest of her cramped up body. Stomach walls pulsed and squeezed her in all directions. It seemed that she might be bigger than Venusaur's regular prey as its stomach had expanded to accommodate her size. Perhaps she was just unlucky enough to find a desperately starving Venusaur.
'At least it'll be for a good cause then...' Krystal thought. It was morbid but she already knew that her chances of survival were slim. She was too squished inside its stomach to even move, much less turn around and escape or fight her way out. Her only hope came from Caleb or their Pokemon hearing her calls for help and coming to look for her. But even if they found the Venusaur, would they see its most likely bloated belly and know she was in there? Could they even get her out in time?
In a last effort to save herself, she screamed at the top of her lungs.
"Help! I'm inside Vensaur's stomach!" she yelled, praying that someone would hear her.
"Saur..." the disgruntled voiced rumbled around her.
Krystal screamed again but began choking. A rush of lightheadedness hit her and she realized that she was using up the little bit of oxygen available to her. It was a good use of it though. However, the growling that had been so overwhelmingly loud before had been replaced by the equally loud sound of gurgling. So there was a great chance that she wasn't heard over that anyway.
The stomach muscles churned against her drenched body and she felt more liquid pooling underneath her. Unfamiliar meal or not, Venusaur's digestive system was still eager to get started.
"Am I going to be digested alive?" Krystal wondered.
She couldn't help being into vore, but she hated that the thought excited her deep down. Her body being compressed into a ball hurt like hell. The putrid, acidic heat was overwhelming. Yet the sloshing gurgles of the very thing killing her made her feel so good. Her eyelids grew heavy and her breathing labored.
She thought of her boyfriend and their Pokemon, how she may never see them again. The thought was depressing but it's not like this was self-inflicted. She just hoped that they'd get out of the forest before suffering a similar fate. However, if they did go looking for her, she feared the worst.
All of Krystal's senses dulled and faded with her consciousness.