LEGO Harry Potter Collection

This achievement is very easy to get. Just follow Nick (the ghost) when he leads you through the castle. He leaves "ghost studs" which you can "collect" by following him. When you have collected 500 of his studs the achievement will unlock!

So I did not get this one before completing the story and after the story, the ghost just claps.

So MAKE SURE YOU TURN THIS EXTRA ON ASAP.

I have now got it but I had to create a second game and play through as quick as possible to get this.

I had to do 3 lessons and 2 levels and then i was being taken through to the quidditich level through the courtard with the fountain. So i could then get the red brick, go and buy for 99,000 (i was making an effort to grab studs before this) and then return to hogwarts. You can then do a very boring "stand under nick as he guides you across the courtyard and gives out studs", when he gets to the quidditch training part, run back across the screen, back another screen and pick up Nick again and follow him again. After around 10-15 runs of this it pops. Boring but least then its done.

Ghost studs are the little see-through studs that trail behind the ghost character when you are moving around between levels. This will probably come naturally and as long as you pick these up as you go you will get 500 easily. Bear in mind 500 is the number you need to collect, they don't have values like the silver, gold, blue and purple studs.

If you want to grind it you can but there really is no need. When you are moving around Hogwarts between levels, just follow the ghost through a door collecting the studs on the way. Then simply go back through the same door and the ghost will be around the middle of the previous room. Just go over to him, follow him again and collect the studs as he moves to where you are supposed to go. Just rinse and repeat until it pops. Unfortunately there doesn't seem to be an achievement tracker or any way to track this in game.