What skin is this called?

need to know, also does it drop as a loot or can randomly appear at Marcus’ vend machine?

For the Maliwan Grace skin, you have to complete rank 5 of the challenge “I just want to set the world on fire” while playing as Maya the siren. This requires you to deal 1,000,000 points of fire damage to enemies. Once completed, the skin is added to your inventory, where you can unlock it.

Having Fallout flashbacks here… Good times, bro, good times.