That's weird with Jack's Mask. I've only beaten the game once (but I've beaten Th Warrior like 15 times since then), and that first time I killed Jack and the Warrior I got a purple Jack's Mask for Axton (the character I was using) and an orange one for Zer0 at the same time. I've yet to get one since then.
QT x314159. glory of power metal is an anagram of Lame Flowerpot Orgy. ~ kirbymuncher