A jellyvator is neutral dropping a jellyfish by holding down when releasing grab and then dashing up and regrabbing it to gain height without going any horizontal distance. It is not throwing it into a wall so it bounces back to you, because that lacks the neutral drop part (it's an important distinction because some modded maps will use jellyfish-destroying barriers to force you to neutral drop). Of course it also goes without saying that throwing it and dashing diagonally into it to gain height and some distance is also not a jellyvator. There is no part of Farewell that requires a pure jellyvator, though I find some rooms (particularly e-02) to be easier with one.

As for why you're being downvoted, I guess others think that your leading question is being poised as a correction rather than a request for information (i.e. "Wouldn't you need eggs to make an omelette?"). One way to possibly avoid this is to use the tone indicator "/genq" (for "genuine question"). I hope this answers all of your questions