The cry always plays, but the timing of it will tell you if you'll hit a seed within you more common ranges.

A little question about that button mashing. So should I try to time those L+A+L+A somehow, or should I just mash them as fast as possible? Because with button mashing I have always heard the cry.

Ok, that will help me much! Thanks. Will test it soon.

The 3.35 was found by counting frames in VBA and testing button presses before and after.

Basically, you'll want to set a custom timer in EonTimer with the following timings:
1. ~3 sec (you'll SR at the end of this)
2. 3.35 sec (you'll hit L+A+L+A at the end of this)
If Charizard/Venusaur's cry plays any time after during the title screen music begins, don't bother checking the seed. They'll be more constant when you get the timing just right. You obviously need to set L=A, but seeing as this allows for faster button mashing, the game will not register L+A+L or A+L+A as three presses if you're doing it at an adequate speed. A+A+A (or L+L+L) is not recommended because it's simply harder to pull off with perfect timing.

Yeah, I have the save for retail cart stuff. I am going for a SD Mewtwo, and hopely get a retail cart one. I have an idea how to do this, but because I don't have Rare Candies yet, I can't test it yet. But yeah, I would really want some advice :p

You needed a LeafGreen save?
Based on what you've done before I'm assuming you want to try retail cart RNG. If you decide to go through with it I can offer some advice, but keep in mind I haven't been able to pull off a project yet.

Borderline impossible.

I think I heard from someone that you have tried to retail cart abuse Mewtwo in FR/LG. How hard is it? I've been thinking of getting FR cart from a friend, so I could test it.

Yeah I can see why. I also grinded to around 40s and battle is easy because I know when what poke protects. Hopely I can get good one.