The question is very annoying and unanswerable.
That doesn't bode well. Subgenres blend often, but there
has to be a notable distinguishing feature to even consider them subgenres in the first place. Otherwise you're just wanking.
The best answer I can think of is:
Death metal riff:
Black metal Riff:
That would probably have been very illustrative if I read sheet music, which right now I don't. Looks like a lot of effort, though; I appreciate it.
hmn.
A black metal song:
Burzum - Ea, Lord of the Depths
I really hope that song isn't sung in English - I didn't understand a word. Hard to tell, because as you described it the "singer" is really a "screamer" (and he also seems to be about 30 feet from the mic, though that may be my headphones or the relative noise level of the track). Apart from that, it sounds pretty much like thrash. Extreme Judas Priest, if you will.
A death metal song:
Bloodbath - Ominous Bloodvomit
I used to have a Bolt Thrower album (long since given away to a metaller friend) and this sounds kind of like that did. I still do have a Cathedral track that sounds like this, for that matter. Probably you'll disparage those two acts for not being hardcore enough, but I think I can pick a death metal act out of a lineup now.
(I see what you mean about the "cookie monstering", too; I kept expecting this guy to start singing "Cookies! Cookies! Cookies for Satan!" at any second.

)
A grindcore song:
Circle of Dead Children - A Family Tree to Hang From
OK, what the
fuck? Sorry to be dissing one of your favourites so harshly after you were good enough to take the time, but how can anyone call this "music" and keep a straight face? The other two tracks you uploaded weren't really my thing, but at least they were clearly and discernibly songs performed by people who knew one end of a drumstick from the other. This sounds like someone dropped a live electric wire into a spastic's bathtub and recorded the results.
I'm kinda dissapointed I uploaded all these before you were so...I dunno. Condescending.
Think how I felt when Misereatur began talking about "the wrong kind of growl for black metal". A less open-minded person would have assumed he was taking the mickey. I might have too, had it been April 1st.
Meanwhile, I wasn't being condescending - just not taking the matter too seriously. "20 Golden Grindcore Melodies" (which is not available in the shops, but call our 1-800 hotline now to order your copy for the low, low price of $19.99) is a recurring gag I pull out whenever the idea of Ronco bastardising and homogenising yet another musical genre is apt. It usually gets a laugh even
without my acting out the lounge piano version of Napalm Death's "You Suffer".
Because you can't understand something doesn't make it beneath you.
Please learn the difference between "don't" and "can't" and when to apply them correctly.