Grabs. My grab game was really ****ty just a few months ago, but after constantly and consciously working on grab setups etc, I think my grab game is one of my top skills, especially against space animals. Unfortunately, working on grab game takes more than a couple days, which it sounds to me is all you have, but these are a few things you can probably implement in a couple of hours of friendlies before the tournament.
Easy grab setups:
1) Tomahawk. This one is so easy, yet so effective. Let's say you hit his shield - remember this situation because I can guarantee you that the next time it occurs, they will put shield up again. It looks kinda silly with ganon, but it works. Usually requires a read, but sometimes you can do it on reaction if you catch yourself before throwing out an aerial when you don't need to.
2) CC --> grab. You actually got one of these on a waveshine, which is really impressive. That's hard to do. But at low %, CCing the weak hit of nair (or even strong hit at certain spacings) will get you a grab. Try to take note of what sort of aerial he's throwing out though because you do NOT want to CC a drill. Getting hit with drill while you're crouching can mean death.
Intermediate grab setups:
1) waveland tomahawk grab. Bizzarro Flame and Renth love to do this. You jump as if you're going to bair, cross them up, and grab. It's so fast they don't know what hit them. Similar to tomahawk, just with a different spacing.
Example.
Advanced grab setups:
1) SDI drill --> grab out of shine. Self-explanatory. If you SDI fox's drill, a lot of the time, you'll get a free grab because they'll shine, even when you're out of range. It's just a habit to them. Anyway, if they do that long drill (usually happens from the ledge), you only need to do one input of SDI and then just hold away and you'll get it. Normally, you need 2 inputs (I use control stick and c-stick) for it, and it works.
2) Shield DI --> grab out of shine. Literally the exact same thing, only in your shield. Same thing applies with the long drill etc too.