There were a few threads suggesting a very low drop rate for the helm in blue for normal Cradle of Shadows at around launch for both PC and console. It didn't drop for me on normal so I can't confirm it.
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Thanks for all the answers guys! I can confirm that it does drop on normal now as I saw it drop for a team mate last night. I'm still 0/7, but I will update when the rng gods find it appropriate to let me get one.
I would say it is about a 25% chance for 1 member of your party to receive the Monster helm from the Normal Dungeon. This is where I received all of my new Monster helms on PC/NA, so I can confirm that it does indeed drop on Normal for PC users at least and I would hope to heck they allowed the same on Console to make it fair for you guys.
They also dropped in Purple when I received them.
The Vet version has a higher chance, like 80% for at least 2 or more people of your party to receive a helm.
Hard Mode apparently gives a 100% chance at drop.
Oh, they can also be traded to the members in your party.