User blog comment:Silkworm Bot/Unpopular opinion/@comment-26268426-20170509160638/@comment-30385427-20170509171746

Psychic was never supereffective against Ghost; it was immune to Ghost, and that was clearly because of a bug (all of the guides and the anime said Ghost types were super effective, so I'm guessing the immunity wasn't on purpose). It was just super effective against Poison, and since the only Ghost types were Poison types, they were weak to even Abra.