Self-insertion into a Muppet-based fanfic is okay around here. We do it all the time, it just depends on the level of how the self-insertion is written. As you pointed out, there are a ton of self-insertion fics floating here lately, I've had to delete a few because they were just plain lyrics with no actual story. But there are very good self-insertion fics from some of the older authors. If it wasn't for Sara (ReneeLouvier)'s Sadie's Stories and Beth (redBoobergurl)'s Rowlf's Stories and some of Lisa (TogetherAgain)'s actual completed fics, we wouldn't have the Hensonville City scenario. Catherine (Ruahnna) is the veritable master of good/excellent self-insertion what with the various cameos certain forum members have had in her grand novel Kermie's Girl, and I myself took the challenge to write a variety of short somewhat inter-connected fics some of which feature my fan-fic self. And I have to mention Kris (newsmanfan)'s Newsie's Stories as well as Kim (Slackbot)'s more Muppet-centric fics as well-written fics featuring either themselves or their own OC's, which is another thing we heartily welcome in our fanverse, again, so long as they're incorporated well. Hope this helps somewhat. BTW: All the authors/fics mentioned above can be found in the 2014 Fanfic Library Index thread.