After defeating Dorothy in your first fight, you will go to the start of the level and make your way past the rooms. You will fight a boss named Spider. Try to move away from the dangling spiders. His weakness is Fire (red serum). When a spider gets on you press R1 (shield) to get them off. You cannot attack him with D-Felon (blue serum). When he comes down from his web, use Fire or Nalcon on him. After you defeat him, you obtain a Skip (allows you to improve a serum ability). Use your Skip on the Nalcon, as it will be needed later. Then, open the gate and cross the bridge to Dorothy.