Trollersprites

[Vic]

Don't ask me if the NES would actually support so many sprites this would require.

It couldnt, since the NES can only display a maximum of 64 sprites (either 8x8 or 8x16px) on the screen at once (and 8 per scanline)
And that kraken thingy looks like it got a lot more sprites going on at the moment.

HOWEVER, bosses of that size can easily done by using tiles, which only restricts the amount of palettes you can use. (4 palettes with 3colors+1 background color, which is the same across all palettes)
A game that does this trick pretty well is "Totally Rad", might wanna check out how the stuff is done in that game.

C&C wise I've got nothing to add, since Previous already said what I was going to say.