Function:
TileAtOffset(x0,y0,dx,dy)
Return Tilemap.tileat(tilemap.positiontotilex(x0)+dx,tilemap.positiontotiley(y0)+dy)
Where x0 and y0 are your original coordinates in pixels (mouse.x,y or player.x,y) and dx and dy is the offset in tile index, which can be any integer -1, 0, 1, 2, ect.