The whole idea of an ereaser has become sort of a thing of the past for me, since Ggale. Sometimes when you erease you want it to use the transparent color of the layer...and sometimes you just want to use a darker color of the material you're drawing on....I find it annoying to have an ereaser that makes that choice for you, I prefer to pick em by myself.
Now, about the PEN thing...why is it not working? I'm always making random brusher for myself with Ggale.
-make a new folder inside the ggale folder called PEN
-make a new 1bpp BMP inside this folder, that is 32x32 pixels of size.
-use black as the transparent color, and white as the color of your brush.
-save the bmp
-go to the palette's dropdown menu, and clik Reload Pen/Tile
-The new brushes will appear after the preset ones in a completely random order...I've never been able to figure out what determines their order.