Gonna correct ya coz you asked for it.Also the Pika+G&W thing was possible in Brawl and not banned iirc (someone correct me if I'm wrong), the video you linked I think is more likely an extreme example due to unfortunate spacing and probably not knowing what to expect (not to mention G&W had two sources of thunder) rather than of the true dominance of the strategy. It is a pretty strong strategy though.
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Pikachu Thunder in G&W bucket was not an instakill in Brawl. If you fill GnW's bucket up 3 times with ZSS Dsmash in Brawl, than that was an instakill, like this. And guess what? It was banned, in some states of the USA (Notably Texas)
Either way you shouldn't ban this thanks