Ralf's not too bad, if you can consistently change the pace and the space of your projectiles...
EX fireball goes through Ralf's qcb+P, except the EX one I believe... If you do your EX fireball before he gets his EX qcb+P out, it will hit-- just know his EX qcb+P has a delay to it...
You can't do too much rushing without following behind a fireball, so just make sure that you have one out, and try to inch in as best as you can.
j.B cross up helps, too...
Try not to do anything that gives him a free b~f+P, because that can lead to some DC combos...
his only real long range pokes are s.D, c.D, c.C, and s.C... Ralf can't rely on c.C too much, except for close punishes... I believe he can go into HD mode from that, so be careful with the rushdown...
For those that are gutsy enough to do backdash into air qcf+P, you can trade or possibly beat with rdp+K...
You can run up behind fireball, use c.D and cancel into backflip, and immediately cancel to fast fireball if they don't jump... Ralf is gonna want to control the ground and make you jump. But just like Chess, you have to make the opponent play your game-- in this case, make Ralf jump...
Situations like the one mentioned above can train him to think he has an opportunity to capitalize on a whiff... If the fireball is fast, it will hit if he tries to be slick and jump... If you've already trained him to roll, you should use the A projectile... If he somehow manages to telegraph and qcb+A, then you can continue to rush, or if you're gutsy, qcf+B/D; but there's a risk if Ralf recovered from his move already... The trick with that is to go into qcf+B/D immediately after the fireball, but that's if you know he's gonna go qcb+P...
Ultimately, it's not too hard to face Ralf. You just have to read him a little more, and then train him to do what you want for the right setup...
Oh yeah, qcf+B/D should punish the dive punch, depending on how high he did the move, which affects where he lands in the end... If it was close enough, just dash in and combo instead...
Lastly, if you've got your opponent to roll past your fireball setups, try something like either s.D or c.D into backflip and cancel backflip into dp+P... This can be risky, but again you have to ready your opponent to determine whether or not this is an option... At the very least, option select so you can break throws...