I currently have collected 10/17 heads for Zer0, and I will be listing them all here with photos.
Zero
M0t0cross Marauder
Gh0st
Nihilism Zero
3ng13
Aliennati0n
DisharmOny
Crafty M0t0cross Maruader
Handsome Jack's Mask
Vault Veteran Arachn1d
Nihilism
3ng13
Gh0st
Aliennation
Handsome Jack Mask
Crafty
Vault Veteran Arachn1d