For trigger tricking, you will not be able to light shield with the button you use to parry. This is the only downside to trigger tricking and it is definitely worth it. It makes parrying much easier. It also doesn't matter if you're using a gamecube or wii, it works the same either way. You want to hold down the shoulder button the
whole way to make sure that you won't get any chance of light shielding with that button.
Having the CPU spam a slow attack is a good way to get used to the timing of parrying, but I don't recommend you start with powershielding because it's a different timing than parrying and it isn't actually useful for Yoshi (reflecting projectiles
is useful, powershelding regular attacks is not useful at all with Yoshi). If you get a powershield, it means you pressed shield 1-2 frames too early to parry. You will see a white flash that looks like this:
As for other ways to practise parrying, the 20XX pack gives you a lot of options. One you get comfortable with the basic timing, try as many as you can think of, since practising a variety of things will leave you better prepared than just practising one thing. Some of my ideas include:
- CPU spam any attack
- Falco CPU short hop lasers (you can also practise reflecting these)
- Falco/Falcon approaching Dair (like Dinowulf suggested)
- CPU out of shield options (you will need to hit them to trigger the out of shield option before you can parry it - this is also good for practising shield pressure but don't worry about this until you're already used to parrying a lot)
Most importantly, practise against real people, because that is the best parrying practice you will get.