Masked Villain Achievement
Modify a mask for the first time.
To be able modify a mask, you must have a blank mask, a material, a pattern, and colors. All of these are obtained during paydays when you pick a card.
This can be done from your safe house or from the menu. From the menu, select "Inventory" and use your bumpers to page over to "Mask." Highlight and select one of the Empty Mask Slots, then select a mask from your Mask Stash. Once you've purchased the mask, press to customize it.
Note: If you have the pre-order Lootbag DLC, it includes the Skull mask, so you only have to unlock a material, pattern and color in the game.