I don't see as much of what I think of as twitter "forms" here (e.g. tweets that take the form of "tfw when you x"). Some possible explanations:
1.The higher character limit obviates them
2. There's a perceived expectation that twitter-behavior should be eschewed
3. People just tend to act differently in a different context and are "starting over" cognitively
4. The set of people who would use those forms is not very coextensive with the set of people who would join Mastodon