You end up back in Hogwarts. Go up the stairs, and up into the dog area. Nice puppy!

Zap the painting. Turn on the lights. Zap the duck to make it bigger, then give it to the dog to play with. See, he's a sweet doggie!

Now build the harp, and go in.

Shoot / scare all the plant life. Work your way around. Surprise! Now you're in the key room!

Shoot all the tendrilly things. Harry (of course) gets on the broom and goes after the keys. Shoot the big key a few times. Then clear the green things in upper right, and the key becomes active. Move on.

A chessboard! This is fun. Hop on horse and ride it. Then hop on the tower and ride it. I wish you could really play. But still, it's easy enough to move along.

Now on to the Final Battle. Is that like the Final Countdown? (Do do DOOO DOOOO)

Have Hermoine lob back the green things while Harry then jumps over and bashes him. Three rounds in typical gaming fashion and you're all done.

bricks:
28 level
29 sip

You see an ending scene in the infirmary - and then long credits ...

Lego Harry Potter Walkthrough