There's a lot of strange religious people who instead of just deciding that some game or show doesn't fit in with their beliefs and that's that, they have to decide it must be "Satanic" for some reason. Mario, Pokemon, MLP, Doctor Who, Dragon Ball. they'll use it for anything they don't like, or want their kids viewing/playing. They'll somehow pick satanic imagery out of anything.
It's not exclusive to religion, honestly. People do that with anything they don't like for whatever reason. "MLP is Sexist!", "Super heroes promote violence!", "Video games cause shootings!", "My son's pet rock turned him gay!". The list goes on.
Pokemon isn't satanic, and neither are any of those other things. Even if it was...What, Satan's hobby is making fun video games for all ages? Seriously, are we sure the guy is actually evil in that case?