I think Jill and Shuma have a decent need for jump cancelling during combos but i dont really know how to do it. Is it just jumping after the pop up hit or is there certain motions or technique required? Also, what characers besides those use it alot?
Nope. It couldn’t really be any different than canceling into another attack button, only this time you tap up or u/f. Just pay attention to the duration of the attack you’re jump canceling.
There are two kinds of jump cancels.
There are regular jump cancels - Amaterasu can cancel her standing H into a jump, MODOK can cancel all of his Hs into a jump, etc. To do these you simply need to hold up after doing the move and it will cancel into a jump for you. Easy enough.
Then there are TK jump cancels. These are when you jump cancel out of a special move, and then do another special move before the jump actually occurs - essentially allowing you to cancel a special into a special (which you normally cannot do, without burning XF or using C.Viper’s ‘EX’ specials).
To do C.Viper’s TK cancel, you would do the motion for the first Seismo Hammer, then do the motion for the second Seismo Hammer just before the window for the jump cancel. End the second motion with up forward + attack button - the upforward will initiate the jump cancel, and the attack button will initiate the Seismo Hammer. Repeat as many times as you want.
:dp:+:l:, :dp::uf:+:l:, :dp::uf:+:l:, :dp::uf:+:l:, and so on
Of course the timing on these is strict (not as strict as SF4, but still strict enough that it takes practice), you need to do the next Seismo Hammer late enough so that the game still recognizes that you did a Seismo Hammer.
I do not how what specific moves would make this practical for Jill, but she can utilize it as her Somersault is jump cancelable.