How do you get ridiculous in LEGO Harry Potter?

Answer 1

Sometime duiring your third year, you will have a DADA (Defense Against the Dark Arts) lesson. There are 2 cupboards in the DADA room with square's on the ground in front of them. You must be Hermione and Ron and use Ridiculus on the boggart. Harry is too scared as his boggart is a dementor (you learn expecto patronum later on). There is a black board near the back left corner of the room. You have to defeat the boggarts 3 times I think it is to unock Ridiculus :) i can't remember too well as it has been a while since I played.. anyway, I hope this helped :)