In the Pokemon Adventures manga, Green Oak is possesed by a Ghastly and forced to battle Red, when they are at the Pokemon Tower. The Ghastly also makes a crapload of zombies from the buried Pokemon there, but Red/Green manages to smash them into pieces...
Pokemon Adventures is a bit more mature than the anime ;O
Well it's not surprising the comics are darker considering some of the pokedex entries in the games -- in the cartoons the ghosts are just depicted as mischievousness (although a gastly does nearly lead Brock and James to their deaths one time) but in the games their pokedex entries talks about them stealing life energy from people and suffocating their prey with gas and that kind of thing.
Yeah, five different regions and seven different leagues and he's still ten XD (I think it's seven leagues, I liked the cartoons when I was a kid but I never watched past the original series, just going by what I've seen clips of).
To be honest I prefer to just play the games though, I kind of have my own "headcanon" regarding some of the characters, and there are three different versions of the Pokémon world in comics -- Pokémon Adventures (with Trainer Red and Blue/Green Oak), Pocket Monsters (with Isamu Akai and Kai Midorikawa who is apparently no relation to the Oaks), and of course there's the comic based on the cartoons, The Electric Tale of Pikachu (with Ash Ketchem and Gary Oak).