The Hitchhiker's Guide to the Galaxy has this to say about Pokemon, among other things: It's an important but very little-known fact that if an electric Pokemon and a psychic Pokemon use Thundershock and Teleport on each other at the same time, it will teleport both Pokemon very far away, and if there is anything in between them, it will also be transported. This is because the Thundershock lends power to the Teleport, and turns the area around the Pokemon into a temporary "Star Trek" transporter. Occasionally, it teleports the Pokemon into an entirely different universe.
Jigglypuff used Confuse Ray on Pikachu! Pikachu dodged it just in time. Frustrated, the Jigglypuff used Teleport just as Pikachu used Thundershock. Jigglypuff, thinking Teleport hadn't worked, used Sing. Instantly, everybody near the place both Pokemon had landed fell asleep. It didn't affect Pikachu, who hadn't come through yet. Way in the future on the Starship Enterprise, everybody was sleeping because of Jigglypuff. The ship was on autopilot. Nobody was about to get up to fix the transporter, which had just gone haywire and teleported two Pokemon on board the Enterprise. Jigglypuff looked around in surprise. "Jiggly." Pikachu jumped. "Pika! Chu!" They were in a very strange place. There were odd machines all around, and an aura of electricity filled the air. Jigglypuff couldn't feel it, but Pikachu could. Pikachu took some electricity and stored it in its cheek pouches for later. As Pikachu took some electricity, a power surge went over the ship. The lights dimmed and the engines slowed down. The window screens went black for a few seconds. Jigglypuff wandered over to the holodeck and turned it on. An image flashed at random. The image happened to be one of Team Rocket. "Jigglypuff!" squealed Jigglypuff. It ran back to the bridge. "Pika chu?" asked Pikachu. (What happened?) "Jiggly! Puff!" squealed Jigglypuff. (Team Rocket!) "Pika…" Pikachu thought. "Chu?" (Where?) "Jiggly! Jigglypuff," explained Jigglypuff. (Come, I'll show you.) It dragged Pikachu to the holodeck and turned it on. This time, it was an image of three firemen. "Pika!" squealed Pikachu, jumping about a foot in the air. Jigglypuff laughed. "Puff Jigglypuff!" (It's just a picture!) Pikachu reached over to turn it off. They wandered back to the bridge. Pikachu looked at the buttons, levers, and screens. "Pika." Jigglypuff started fiddling with the teleporter. The teleporter suddenly hummed to life and teleported a pile of books onto the ship. They fell over with a crash. "PIKA!" screamed Pikachu. It let loose with a Thundershock that a Graveler would have felt. The lightning bolts from the Thundershock reached toward the engine and hit it with a sizzle. Pikachu had fried the warp drive. The ship spun erratically off course. It created a spacetime rift and fell through it to the planet Earth, circa 1999. With 200 yards to go before it hit the ground, Jigglypuff used Teleport again. The ship vanished into the margin between universes and ended up on the world both Pokemon had just come from. The ship landed on a huge, sharp rock, which tore a hole in the ship's wall. Pikachu and Jigglypuff ran out through the hole to find Ash, leaving the crew of the Enterprise, who were just waking up, to deal with the Pokemon that had decided to investigate this strange new thing. When the crew woke up, there was a Snorlax playing with the warp drive. An Ekans was coiled around several of the levers, and a Jynx was experimenting with the holodeck. There were Pokemon all over the place. I won't tell you how they got all the Pokemon out (it had to do with the fact that there were a lot of Pokemon trainers around with a lot of Pokeballs they needed to fill) or how they got off the planet and back into Star Trek (I have no idea how they did that). But I will tell you this: two days after they got back, they found a nest of Rattattas in the cargo bay.
The Hitchhiker's Guide to the Galaxy says this about Rattatta: Rattatta are a species of Pokemon. They look like vicious rats, hence the name. They are found almost anywhere, and their only moves are Growl, Tackle, Bite, and Tail Whip. Their evolution is Raticate. They reproduce almost as fast as Tribbles.