Things get a bit funny with Pokémon because of what has been literally banned (versus effectively banned), for what reasons, and for which format(s). I won't have time for a thorough write-up of all of them, but as a taste of things to come, "Ancient" Mew may never have officially been banned. J-Wittz is correct that it was not legal for competitive play when it first released, and probably by the time he made the video, but it was legal for a period and it was all about local language rules. Pokémon only allows you to use cards from your area's accepted local language(s), both when the card first released and now. However, there was a stretch of at least a few years where you were allowed to use foreign language cards so long as you had an acceptable reference. Ancient Mew is written in the made-up "Poké-Glyphics" language, so it always counts as a foreign language card. During the period where foreign language cards were legal with an acceptable reference, it was legal. Once this became too much of a hassle (for foreign language cards across the board) and the floor rules changed again, like all foreign language cards Ancient Mew once again became illegal to use. So it was effectively banned, but never actually banned.
I'll try to find time to explain the circumstances around the actual banned cards (plus _____'s Pikachu) when I can. I have to leave to help a friend soon, and won't be back until evening, today... at which point I probably won't be firing on all cylinders. XP