If you do a 9 jump you can follow up the J623B with 2B>8jump>jb>j4c>9jump>JC against most of the cast in that combo. The dash under is useful for Ragna, Tager, Rachel(that last JC whiffs on her) and I think Carl though.
After the last JC if you've conditioned your foe to instantly grab any chance to get out of the corner you then can do a B nail and then go right in and do a 5C, if they jump the explosion will hold em in place and you'll usually hit em with 5C since people don't usually barrier at that part, some people don't even notice the explosion so you doing that will instantly pick up the combo off of the explosion and that's an amazing starter, you can go into 6D>623B>stuff after that.