el-remmen
Moderator Emeritus
I just doublechecked.
Psionics is CORE in 1e (PH and everywhere else).
Core? It was included in an appendix in the back of the book!
Psionics is CORE in 2e (MM).
It was added as an optional splat book.
I don't remember 4E.
I don't remember it being "Core" in 3E either and it may be in 2024 5E given the inclusion of psionic classes - but that hasn't come out yet.
In addition, in the culture of D&D playing for decades, my experience tells me that the inclusion of psionics was not a core part of play - but an add-on. But we are just gonna have to disagree about what "core" means.
Personally, I have used psionics plenty (2E being my favorite iteration) but I prefer it as an add-on and never saw it as more than that.