@GossiTheDog Hi. I've been running a Mastodon instance in Korea, and these kind of accounts have been coming to my instance several times. Usernames are random, email domains are random, they're using VPN too.
However, I think they didn't know that Mastodon has a feature of checking email domains. So I've managed to block the exact MX record of their email domain, then it stopped. For awhile.