I have checked the original video at nico nico douga to check the Japanese comment.
The video description say something like "I have tried to make a not too easy, too hard moderate stage.
A "usual person" (there probably a better translation) who never tried it challenged it."
Of course in the comments there's a lot of "Wait, what?!", "lol", "eeeeeeeehhh!?".
At the part with the fairies, there was some "Master Spark!?" and also "The fairies are horrible!" X D
When the player finally clear a part that killed him a lot, there is a lot of "Oooooooohhhh". ^^
Many people said "Wait, what!?" at the killing 1up as well as some mentioning it was homing.
At the end, when the player is killed the first time by the boss coming,
you can see him switching to the various game over options quickly.
The text at the bottom say :
"At this point, my friend started getting mad/crazy."
I'm not sure he will be his friend for long. X D
Anyway, during the Marisa fight, there was some comment about how it was pretty
and also a few comment about liking the BGM.
There was some comment saying "NULLITY". Maybe it's its name? You probably know better than me. ^^;
After many failed at temps against the Great Wall spellcard,
the video started to record at the beginning, the comments said stuff like "No way!" "He beat it?".
When it reached back the Great Wall spell card, some people said "Kita" (at last/it came).
When he finally cleared the stage, there was a lot of 888888888888888888888888888888
because seriously, the player was awesome. : )
Oh, now that I think about it the description for the last difficulty level, "Heaven Mode" basically say :
"UWAAAAAAAAAAHHHHH!!!" X D