RE: why are there Yugioh clans
I don't think they're enemies. It's just two different games, that's it. Pokemon was already losing people when Yu-gi-oh came out, if that's what you're getting at for the reason to call them "enemies."
I think that since this is a Pokemon forum, only things that are about Pokemon should be discussed in ALL forums EXCEPT Miscellaneous Stuff since that's Miscellaneous. But that's entirely up to WPM, so it might be fine in the Clan Section to him for all we know.
Arcanine out.