Call of Duty: Black Ops 3 Zombies (DLC #4 Salvation) - Wardrobe Change - In Revelations, wear three different hats. [Bronze / 15G]

There are much more than 3 hats / masks. Here are the easiest three you can get relatively early:

#1 - Wolf Hat
Go to the "Der Eisendrache" part of the map (with the pyramide) and turn on anti-gravity by standing on the four tiles on the floor. Now throw a grenade at the wall opening near the pyramide. A skull will fall down. Feed the skull by killing zombies near it. You will hear an audio cue when it's done. Get the hat from the "Kino der Toten". It's on one of the mannequins.

#2 - Al's Hat
Can be found in the "Mob of the Dead" part of the map at any time. No special requirements, just pick it up.

#3 - Summoner Hat
Build the summoning altar, then summon a keeper and let it kill 20+ zombies. When you hear the audio cue the hat will show up on a mannequin in "Kino der Toten".

You must wear 3 different hats in one match! When you start a new match the progress will be lost and you have to get all 3 again.
The hats also give you upgraded purple perks which makes them very useful items. More hats can by unlocked by killing certain amounts of each enemy type. For example: killing many Margwa's will give you the Margwa hat.

---