How do you fight rank 3 in undernet 4

Assuming you can make it to Undernet 4, take the left path from the square with the pillar to the warp point. Go along the green level to a second warp point, and take that to the blue level. Warp around until there is a ramp. Go down it. There will be a cutscene. As to technique, figure it out yourself--that's what the entire game up to that point is for.