@Wander I know of a situation where followbots made by trolls appeared on Ukrainian Mastodon instance claiming to be "Ukraine Nazi".

This was an attack on open registrations server because trolls knew moderators were offline due to outage, but admin had a lot of trouble asking other instances to lift defederations afterwards, and I have personally seen fediblock posts saying to not hesitate and block by domain (though person who posted it was nice to edit post when I pointed out misunderstanding)