FFII - Help needed! Stuck in Mysidian Cave.

I'm on floor B1 of the Mysidian Cave, and I'm trying to get past the Doppelganger at the bottom left-hand corner of the floor. Apparently, one is supposed to use the Black mask and it makes him disappear. Though when I interact with it, no screen where I can use the item comes up, and the doppelganger just moves around a bit before it returns to its original position. I have also tried using the Black mask from the item menu, while facing it, but that doesn't work either.

I have looked at a few walkthroughs and they haven't helped me with this problem I'm having, merely saying to use the black mask on the doppelganger, which I already knew in the first place. Anyone know what I'm doing wrong? I'm desperate!

By the way, I'm playing the version on Origins, if that makes any difference at all.

Did u place the white mask on the Statue In Town?

Silly me, I haven't! I suppose I have to do that before I can use the Black mask on the doppelganger then? :p

yes

I don't remember. I play FF2J very little, as it's leveling system pisses me off just thinking about it. I'm in the Jade passage but I forgot where or why or what the hell I was doing there.