Draw it with draw_mode7sprite (one of the engine's scripts). The obj_antagonist draws itself that way, so you could just copy its drawing code:
d3d_set_lighting(false)(Keep in mind that it assumes the sprite's origin is in the bottom center when aligning it to the 3D world)
draw_set_color(c_white)
draw_mode7sprite(spr_antagonist,0,x,y,z)
setup_game_fog()