>more nuanced rules
Tulpa discussion isn't banned, and a tulpa thread would not be against the rules. That means discussion of tulpas, guides about tulpas, anons posting progress report on making tulpas or giving each other advice on tulpas would normally all be allowed.
tulpas posting as themselves is not allowed (no rp, GR14). You can talk about your tulpa, but your tulpa can't front and post for you. This may a slightly less intuitive interpretation of the global rules than the rest of the points below, but unfortunately it's impossible to reliably and accurately distinguish between a genuine well-developed tulpa and someone purely LARPing, so if the latter is to be banned as per GR14 (which it is), the former cannot be allowed either.
non pony related tulpas are not allowed; if someone mentions off-hand that they have non-pony tulpas that's not worth chasing up, but any discussion about them would be off-topic (GR2, GR16).
shapeshifting pony-based tulpas that have humanized shapes are only allowed insofar as they are a pony tulpa. Again, just mentioning that it can take a humanized shape isn't banworthy, but in-depth conversation where the humanisation isn't incidental (e.g. advice on how to visualise a humanised form) would also fall under GR2/GR16. Goes without saying that posting humanised images is an unambiguous GR2 ban.
In short: tulpa discussion is allowed, but is not exempt from any of the global rules
, which I would hope should be self-evident. For instance, aside from the specific points I mentioned above, someone going full schizo and posting incomprehensible ramblings would be moderated under GR5 (low quality posts). But this is also true outside of the topic of tulpas - just as all the other points I mentioned above are.
I believe that hopefully, the global rules should be clear enough for this to be self-evident, and that the tulpa thread shouldn't need any special case rules. Anything that would be too low-quality, schizoid or otherwise against the rules everywhere would also be against the rules in the tulpa thread, and vice versa.
Let me know if you disagree, and if you foresee anything that would be GR-compliant but you think could still cause a problem. Ultimately, the rules can always be revised if such issues are discovered. However, I'm hoping that the current rules are worded well enough that they should last a while without needing amendments, including both in tulpa threads and otherwise.