Not much about it has been revealed as of yet other than the fact that the Legendary Chalice will be returning as a new playable character going by 'Ms. Make sure to check out our other Cuphead guides for more tips and tricks. Cuphead: The Delicious Last Course is an upcoming DLC coming when 'they are confident' the DLC will delight the community the way its meant to. Hopefully, having these written out, or the couple of tips within, have been of some help. This guide being cut and dry was no exaggeration.
Let your EX meter fill all the way up (5 cards) and press the EX shoot button to unleash your currently equipped Super Art. It's easiest to practice parrying on the pink spiked balls in the first run & gun stage. Learning to parry is your key to success pushing through the game since parrying gives you 1 EX charge.
In some games, there's a slight delay between jump -> contact -> parry but here in Cuphead, there is no delay and it must be done at the exact moment of contact. The game goes over this a bit, but it's tricky to actually do as you have to jump and press the jump button again right as you touch a pink projectile to parry it. You generally dash more often than you use your EX shot, so it may be more comfortable to have dash set to B (XB1)/Circle (PS4) and EX shoot to Y (XB1)/Triangle (PS4). One tip I do want to mention is that if you are having trouble with the controls using a controller, things may be easier if you swap the buttons for dash and EX shoot.
This guide's pretty cut and dry and covers the default buttons/keys for the keyboard, Xbox One, and PlayStation 4 controllers (for those using a PS4 controller on their PC).