In this level you’ll need a Regular Wizard and Dark Wizard.
Shoot the clam on the ground close to where you start the level. As you swim right, shoot the clam in the background. Go through the tube and pull down both sides of the seaweed on the rock. Shoot the balloon-like creatures that appear shortly after. Swim left and shoot the clam that sits on top of the chain. Continue going left and shoot the skeleton with the chest to get the character token for Harry (Lake Task). Now go right and shoot the clam in the background near the boat. There’s another clam in the foreground, behind some seaweed. Swim down and destroy the barrier from the tube to climb through. Shoot the clam here. Go back and levitate the oars to the skeleton in the boat, and have him row back. The Student In Peril should appear from the hole. Go back to where you were earlier and some tentacles should appear, blocking you from getting through. Work with the other character to unwrap the first two tentacles, and the last one should unwrap itself. Swim forward and shoot the clam in the background, then climb through the tube. Swim left and shoot the clam in the foreground before continuing. Pull the seaweed on the next rock and shoot two more balloon-like creatures. The final clam isn’t far ahead, on top of the rock where the fish tail sits. Shooting it will give you the Ravenclaw Crest piece. Put the fish together and it will destroy the rocks ahead, letting you into the next area.
Shoot behind the seaweed as you enter the area to get the character token for Guitarist. Swim to the bottom area and levitate the fence to get through. Levitate the crab onto the purple platform to let the character on the top through, then switch to that character and shoot the squid’s eye to make it leave. Use Lumos to get through the ink (clearing all of the ink away will get you the Hufflepuff Crest piece). Swim up and to the right, destroy the red plant, and put the pearl into the clam’s mouth on the bottom right to continue.
Swim right and levitate the first chain. Put the seaweed onto the rock and shoot the balloon creature that appears. Swim left and use Lumos on the vines, then levitate the chain and put the seaweed onto the rock. Shooting the final creature will earn you the Gryffindor Crest piece. Destroy the barrier from the tube, climb through, and shoot the chest to the left for the character token Krum Shark. Go right and levitate the ball onto the scale, then levitate the chain. Shoot the silver circle on each chain to free the characters and end the level.
Have a Dark Wizard destroy the chest at the start of the second area with Crucio to get the Slytherin Crest piece.