It is actually easy to participate in Lemmy from Mastodon. Federated community are represented as user. When someone write on the community, they appears as the author on Mastodon while the community boost the post. This way a Mastodon user can follow acommunity. By mentioning the name of community in a post that is not an answer to another post, their write post on the Lemmy community. The next post in the Mastodon thread will be treated by Lemmy as comment.
The problem is more in sharing comments. After one or two level of comment it is becoming very buggy. For the rest, it works very well.