From what I understand, 420chan wasn't shut down, the owner was just a hippie cunt who fucked off.
I dunno where you'd go for talking about substances, not sure anyone here cares enough about that to talk about it, but you can use >>>/pco/ as an alternative to their hentai board.
>>429824 Yeah, Brennan shot themself in the foot and got shot in the other foot........ actually I realized halfway through typing that's a badly chosen figure of speech. Didn't go with Lynxchan (smart), didn't go with jschan due to a tantrum over a petty licensing triviality (dumb) and went home to write another imageboard with blackjack and hookers. Then some drama and legal complication about their mission to get the server back happened (picrel, late May). And then a month ago they bought another niche imageboard for furries. So I wouldn't hold your breath.