Emulator

Game Name?
Super Mario Galaxy
(2 as well, see additional info)

Game ID?
RMGE01

What's the problem? Describe what went wrong in few words.

Roar effects don't show for most people. In my tests, they darken the screen for the duration of the roar.

What did you expect to happen instead?

A shockwave-like effect which starts with the sound.

What steps will reproduce the problem?

1. Start a new Super Mario Galaxy game or begin the first level again
2. Finish the first level and fight the Dino Piranha
3. When you crack its shell, it will roar. There will be no shockwave effect.

Dolphin 3.5 and 3.5-367 are old versions of Dolphin that have
known issues and bugs, so don't report issues about them and test the
latest Dolphin version first.
Which versions of Dolphin did you test on?

For my personal testing today, I tested SMG on 4.0-5672.

Does using an older version of Dolphin solve your issue? If yes, which
versions of Dolphin used to work?

No

What are your PC specifications? (including, but not limited to: Operating
System, CPU and GPU)

AMD 270x
Intel i5-3570k
Windows 7 x64

Is there any other relevant information? (e.g. logs, screenshots,
configuration files)

This likely translates to SMG2 based on my past experience, I haven't recently tested thish. Here are videos, however, that show it pretty well:

Bad:
http://youtu.be/jZC02AAZ4xY?t=11m11s (Bowser, SMG, 4.0.1)
Good:
http://youtu.be/KELFYCIJrM4?t=34m29s (Bowser, SMG, Wii)

Bad:
http://youtu.be/_WK7eWBoAqA?t=6m2s (Dino Piranha, SMG, 4.0.2)
http://youtu.be/YVXoi3BB7bg?t=26s (Dino Piranha, SMG, ancient build from 2009)
Good:
http://youtu.be/KELFYCIJrM4?t=13s (Dino Piranha, SMG, Wii)

Bad:
http://youtu.be/ZeRPJQbWRJ8 (Giant Bowser, SMG2, 4.0.2)
Good:
http://youtu.be/7xNzQyG7ZEw?t=29s (Giant Bowser, SMG2, Wii)

(another random, good quality effect on SMG2)
Good: http://youtu.be/Mtn75w1SjeQ?t=34s (SMG2, Wii)

I unfortunately have no footage of my own, but can confirm the problem also exists on my hardware.