But I've been trying to beat the Strikers Cup, and frankly, I'm at the end of my damn rope. My current team is...

Diddy
Monty Mole
Boo
Boo

I've learned to do the Boo Deke, Belgian Waffle, Mid-Court Chip, Monty Deke, and Jump Deke shots fairly reliably. I can make it to the end of the Elimination matches before the AI starts pulling shots out of their asses, but have no idea what to do when it gets to the point where essentially every shot they shoot goes in.

I just ended up quitting in disgust earlier after a completely ridiculous situation occurred. I was tackled on the opponents side of the field, and the ball rolled all the way across the field and into my goal. I was about ready to break the game disc in half, and I'm currently contemplating getting and SD card to download a game save for Petey (Only reason I'm bothering with this moronic cup), but figured I would see if I could get any decent advice.

Are you having trouble scoring shots or getting scored on?

I don't usually have much trouble scoring if I get a chance too. It's just the problem that occasionally the AI goes on an extreme offensive and I can't really keep the ball for more than a few moments. Generally this is followed by several shots on my goal, most of which go right by my goalie (as I said, I had one simply roll into the net from the opposite side of the field).

The ball rolling into the net is just bad luck. I would try taking your Monty Mole and hucking people into the fence, throwing off their offense. You don't have a lot of defense, so it might be a bit rough, but I'd start out with that and see how it gets you.

The thing about Striker Cup teams and Level 5 computers is that they foul like bastards. They take shots they normally wouldn't take, but their strength comes from the strong shooters.
You have to learn to fight fire with fire and learn to pick out fouls. That is, if his strong shooters are scoring relentlessly, go ahead and give him some of the business yourself.
If you can play trickier offense than the computer, you can usually win if you can pick your fouls well.
Two Player can help if you learn to work together to perform things like Belgian Waffles, though like you saw the computer will sometimes pull something out of it's ass.