HuC's map_get_tile() function seems broken, but you can use vram[] instead.

e.g., tile = vram[y * BAT_width + x] & 0x0FFF;

The above code would get the tile at x,y (8×8 tile coordinates). BAT_width is the width of the virtual screen (32, 64, 128). The & 0x0FFF part strips out the palette data so you are left with just the tile number.