I have the RED mutiny helmet. It does have vents and I keep them open at all times.
I do not wear anything around my neck or face as I run hot enough as it is now.
I've never seen the Mutiny up close. It says there are "hidden vents"... I sure can't see them on the website.
I wear glasses so I really can't have fogging. This season I am using a Giro Seam with the "stack vent". It's an always open vent at the front of the helmet that lines up with the top vent of my goggles (VZ Feenoms). Once in motion, zero fogging.
Have you tried any other helmets?