do you think ectobiology was a necessary sburb mechanic for everyone who enters the medium plus a relative, made necessary retroactively via a scratch occurring, or something confined to universes A and B/lord english's alpha timeline? sorry if this is a complicated question - trying to get all angles for a fansesh and i'm not a fan of handwaving

Only the main SBURB Session of a Planet needs to have any Ectobiology, since it’s the Session that sends out the Frog Temple, it needs to be played in the first place, so the Players are retroactively engineered. Not needed outside of main Sessions- Unless you mean Frog Ectobiology in which case, it’s necessary in every successful session.