1) Okay, so the comments penalty is especially strong. Sorry. 2) I don't think that downvoting a comment on a submission will affect that submission's ranking.

1) Okay, so the comments penalty is especially strong. Sorry. 2) I don't think that downvoting a comment on a submission will affect that submission's ranking. If you leave a bunch of spurious flags the moderators will disable the flag feature on your account, though. (Happened to me) 3) Assuming a pool of colluding users, this would actually be a plausible attack-- except that HN's userbase is tiny, and the moderators are active. Voting rings show up easily, but I don't know if they're looking for "comment rings". An easy technical solution would be to ban users with "throwaway" in their name from commenting on submissions.