GLSL ES; use with matrix_set and any of the draw_sprite functions in GameMaker. Fragment shader is just the passthrough shader.

billboarding.vsh

attribute vec3 in_Position;                  // (x,y,z)
//attribute vec3 in_Normal;                  // (x,y,z)     unused in this shader.
attribute vec4 in_Colour;                    // (r,g,b,a)
attribute vec2 in_TextureCoord;              // (u,v)

varying vec2 v_vTexcoord;
varying vec4 v_vColour;

void main() {
    vec4 object_space_pos = vec4(in_Position, 1.);
    
    mat4 worldView = gm_Matrices[MATRIX_WORLD_VIEW];
    worldView[0][0] = 1.;
    worldView[0][1] = 0.;
    worldView[0][2] = 0.;
    
    worldView[1][0] = 0.;
    worldView[1][1] = -1.;
    worldView[1][2] = 0.;
    
    // comment out this bit for cylindrical billboarding
    // (you may wish to have a shader uniform to determine this)
    /*
    worldView[1][0] = worldView[2][0];
    worldView[1][1] = worldView[2][1];
    worldView[1][2] = worldView[2][2];
    */
    worldView[2][0] = 0.;
    worldView[2][1] = 0.;
    worldView[2][2] = 1.;
    
    gl_Position = gm_Matrices[MATRIX_PROJECTION] * (worldView * object_space_pos);
    
    v_vColour = in_Colour;
    v_vTexcoord = in_TextureCoord;
}