Was practising on digital drawing and suddenly this appeared!

I tried shading him in grey but all of a sudden when i multiplied the layers a bunch of white and darker lines/spots appeared from the layer where I was drawing on, and I have no idea how they got there, since they were invisble untill multiplied or the background erased black. Nor did I know how to fix it without earsing my entire drawing.

Anyway, my orc Greggar again!