All the time because I was bored. It usually depended on the game, although I've done the following themes before:
- Elements. (First Red team)
- Card Captor Sakura Clow Cards. (Current Red team)
- Japanese names of human Pokemon characters. (Current Fire Red team)
- Japanese names of anime characters in general. (First Sapphire team)
- Stones. (Current Silver team)
- Herbs/Food. (Last Silver team)
- Gods/goddesses. (Current Crystal team)
- Colors. (First Silver team)
- Philosophers/writers. (Current Leaf Green team... although it's a challenge team involving a character I RP anyway, meaning I sort of have to.)
However, for Sapphire and Ruby, I've recently taken to just giving random names to my Pokemon. The main explanation is that I've just given up trying to come up with names that went in a pattern. That and Ruby is currently hosting a challenge team involving using James's Pokemon, so to be accurate, I decided not to give the Pokemon I used nicknames.