Yes. You can enable "showdead" in your profile to see [dead] comments hidden by default. Comments end up [dead] when they have been [flagged] by enough other users, when the user has been explicitly [banned] by the mods or if the user tripped an automated system (bot detection, sockpuppet of a banned account, lots of [flagged] comments...)

If you think a [dead] comment would contribute positively to the conversation, you can vouch for it, in which case it will become visible to everyone once enough people have vouched for it.

Yes, but primarily for new accounts: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu....

Once an account has an established history, we say publicly that we're banning it: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...

Seems like it. I think I'm shadowbanned.

@dang Is that so? Why?

You're banned, but not shadowbanned, because we told you here: https://news.ycombinator.com/item?id=26930848.