Funny Flat Fish

I found this fish in Lembeh. I know it's some sort of flounder or sole, but otherwise, I've never seen anything like it.

It was about five to six centimetres long (two to two-and-a-quarter inches), and changed to a dark grey/ brown colour after some time.

Besides the bars on its body, the large mouth relative to body size is a distinguishing feature.

Anyone know what this is?

flat fish