Yukkuris are disembodied heads... they are believed to be magical... they want sweet-sweets like the pagan tradition of Halloween... they seem to convey the negative feelings around them...
NOW EVERYTHING MAKES SENSE. ...and I'm not even surprised, I mean... it should have been obvious: yukkuris are the devil's spawn.
In b4 a Doom Custom Wad that remplaces all the monsters with types of yukkuris and clearly state that yukkuris come from hell, aka not like that "custom wacko wad" about Gumshoe gunning down a lot of shit incluiding yukkuris.
Actually, yeah, I've been wondering that for a while... this, the starcraft ones, the yukkuri shields have all been uploaded by snake and are of similar style, and there's no other source. You drawing these, snake? I think so, but I'd like to get confirmation...