Your first fight is against Peacock. As a warning you, Painwheel is currently the strongest and bulkiest character in Skullgirls. I can hardly help with these fights since Painwheel's slow movement makes combos unpredictable. However, I suggest you try to use w.HKx4 (Walking High Kick four times rapidly) twice in a row to do a good amount of damage. Just try and mix up your combos a bit.
Your second fight is against Ms. Fortune. Against her, I typically spam MK (Middle Kick) to knock her up into the air, then spam buttons after jumping to get some good hits in.
Your third fight is a mirror match. Spam buttons and see if you can find which move works best against her (usually, it's different every time). Once you find the attack that works best, use it to it's full extent.
The fourth fight is up against Filia. In this fight, unleash the beast inside of your and mash those buttons like they owe you money. Do NOT let Filia attack, she also hits hards and has some very long combos.
Your fifth fight is against Valentine. Just like in Filia's fight, unleash your full fury and get crazy. Valentine has very long combos that don't hurt much but they sure do stack up overtime.
Like usual, you move down to the basement of the Grand Cathedral to find Marie. Click "Next Page" for the guide on fighting the Skullgirl Marie.