Since there are so many sidescrollers about jumping around already I wanted to try to put less focus on that aspect in this game, also, it's not like mages are famous for their athletics. So the way jumping works is a bit of an experiment: You jump when you release the up button. The longer you've held it down, the higher the jump (up to 1 second or so). You also cannot change your momentum while in the air.
I'll have to see if by explaining it better and implementing the celeste platforming tricks it becomes tolerable. If not, I'll just give up and implement standard jumping.
I'm not sure what exactly you mean by up and down movement, but if you mean something like the last stand (flash game) I don't think I will go there unless coming up with levels becomes too difficult with how things are now.