All Bonus Stages

These are pulled (and slightly edited) from the gamefaqs page contributed there by user gs68: https://gamefaqs.gamespot.com/snes/588362-gradius-iii/cheats

Stage 2- When you see a hole in the wall at the bottom of the screen, fly down there.
Prerequisite: None
This stage does not seem to have any use in speedruns since it comes right before the boss.

Stage 3- When you reach the lower level of the stage directly after the active volcanoes, there is a platform in the ceiling that drops down. When it drops down, fly just below the part where the platform was.
Prerequisite: Destroy all of the dispenser enemies (the ones that spawn other ships) in the stage up to that point.
This bonus stage saves a massive amount of time over finishing the stage normally, don't miss it.

Stage 4- In the last set of Moai heads , there is one laying down faced up which will lift itself up. Fly behind it.
Prerequisite: Nothing must be highlighted on your powerup bar.
I found this one to save about 3 seconds in my regular Easy runs, worth it if you can get an early entry, though I haven't entirely tested how much difference the time of entry affects the time saved.

Stage 5- Fly just below the ceiling before the narrow corridor.
Prerequisite: The hundreds digit of your score reads 3, 5, or 7.
This is useful for speed only runs, though is still slower if you can kill the boss fast.

Stage 7- Just after the long downward slope in the second half of the level, stay close to the ground and fly into the indent in the wall that comes up.
Prerequisite: Fly through the smallest gate.
This one is useless as it is so close to the end of the stage.

Easy speedrun tutorial

Kinda bare bones, focuses mostly on boss quick kills and a little bit on lag reduction.
https://www.youtube.com/watch?v=GvuTfTi2taA

Name	Author
All Bonus Stages	EODTex 3 years ago
Easy speedrun tutorial	EODTex 5 years ago