Okay, it's time to pull them all. I can draw, but I'm honest, I'm not a real Smeargle. So when it came to drawing something for this project I had to deal with it in some other way. Therefore, I decided that I would start with existing drawings I got from the internet and I would change them according to my idea. When working with several separate drawings, they can be combined in a single collage.
Find the best Pokémon for your characters. Some will be obvious, others require further thinking or research. For example: I found the Rocket / Groot combo box when looking for Google Images.
Use one of the many pokédexes (or is it Pokédices) available on the internet. to look like the nature they should be. Sometimes it involves many adjustments, sometimes a single accessory can do the trick. Again, for Rocket / Groot combo I only needed to change pose (Rocket already had a blaster), because I wanted them to be in the characteristic pose with Rocket on the shoulder.
Print the line in the drawing you found in a very light gray. Now you can use regular pens to draw your design with adaptations on top of the original. This should make your life easier if you didn't use a computer. To change a pose, just print a second copy and cut and pass parts to change the pose. Use a scanner or even your phone to make a digital copy again.
When you have all your characters, it's time to combine them into a single collage. Probably you need to make some adjustments to some characters to get the best results. Think about who should be, what is it that you like to visualize. For "Pyroarkongen" this meant the characteristic scene where Simba, Timon & Pumba cross a tree trunk while Simba grows up.
Now is the time to add the remaining parts. This will probably be the landscape and extra accessories to make the whole complete. Don't forget to download a Pokémon font and add a catchy title somewhere.