A novelty account is one made for a specific purpose/type of comment. For instance, badwatercolor makes bad watercolor. Their usernames are exactly what they are.
A novelty subreddit is easier to define as what it’s not. It’s not for ‘useful/objective topics’ like !firstname.lastname@example.org or science. A great example would be this sub or like Ask ouija. Less good examples are ask lemmy.
Can also feature novelty instances, but none exist at the moment nor are forecasted to existed.
When you find a novelty account/sub that is not specifically troll/spam related, share it here. The sub should be newish or have some sign of life.