Mask Woman, or MYN-001, is an Ogerpon Reploid. . . Who was Yukis, a Yveltal's very first creation, sometimes she refers to him as doc instead of master
She has the 4 masks Ogerpon has, Teal(Grass), Hearthflame(Changes her to Grass/Fire), Wellspring(Changes her to Grass/Water), Cornerstone(Changes her to Grass/Rock)
Then Yukis made more masks, that being the DualGear Mask (Enhances her Double Gear System. Which is Speed Gear and Power Gear) and DiVE Mask 

You can also call her Mimi as a nickname