Apparently the skull meter just represents toxicity and that website had incorrect information
This is the skill you need to get to do that special attack you was talking about
The adrenaline points, the dashes that fill up when you attack and deplete when your attacked indicate when a special attack can happen. I think they have to be full and red. There seems to be some confusion about this across the internet.
There is also an option to make the special attacks happen automatically as no one can seem to pull them off with consistency themselves. But yea the skull meter is your toxicity as I understand it, like if you're being poisoned etc.
So ignore that post.