I liked this challenge. I did it more for fun than winning or anything.
The time-space witch vs. Medusa.
+Beautifly- Yuuko is constantly drawn with or represented by a butterfly. I went with Beautifly instead of Butterfree simply because the style and colors matched better.
+Lunatone- I think Yuuko would best be represented by psychic types. And how many times is she shown looking at a moon? (lots)
+Alakazam- Another psychic type. In appearance and even a little bit of her personality reminds me of Sabrina too. And I liked the picture of Alakazam better than the one I found of Kadabra.
+Haunter- Remember that Haunter from the first season of Pokemon? I imagine Yuuko getting along quite well with him.
I reeeally wanted to add Minun and Plusle as representing Maru and Moro but it simply looked too cluttered.
+Seviper- Obvious (if you know the series).
+Sableye- Kind of a sneaky, dark Pokemon. Reminded me of her.
+Ditto- Probably seems a little abstract, but when I remembered how Medusa took over a young girl's body, the theme of "changing appearances" and her ability to adapt seemed to match up quite well.
The Pokeballs at the bottom were a last minute touch. It reminded me of the games, how it always shows the pokeballs in the lower left corner.
This was the first style that popped into my head so I went with it. But I really want to try to make a Pokemon stadium background, so there may be another one of these, with different characters of course.