Same issue. Advice appreciated.

Apparently using fang and going to the right side of the gold statue is the way to get it.
I've read that it takes a few tries, but that is the way to get it. Good luck, hope this
helps.

Just managed to get the crest using the method that I posted, so it does work.

i used ron weasly but it took alot of tries but i had to keep ahead of the demontors and
remember to keep to the right and run behind the statue before they got me it was really
frustrating

Try it in two player mode. I tried over 50 times in single player with a different
character every time. I tried it once in two player and got it! Have one person take off
as fast as they can, go behind statue on right side. The other person should just walk,
let the dementors get ya. The screen splits and it seemed like the dementors couldn't go
faster than the person walking and dying. Good luck!

2 player mode works great! I did it by myself, had the 2nd controller join right before
the last battle with umbridge and just leave the character alone. Run ahead and the 2nd
controller will keep the demeantors way behind you. I used ron and just went really slow
around the front of the statue and to the left to get the piece. I had tried it over a
dozen times with different characters and got it the first time in 2 player mode!!!

The easiest way to get it is in story mode, you do not need 2 player mode. The best thing
to do is go in options and brighten your screen, that helps a lot. This makes the area
really view-able. You only have the characters you start game with and you do not need
fang. When you start the run, after a few seconds switch to other character, he is in lead
and then just go easy stay to the left, and you can go around the statue fairly slow,
don't run or jump because if you hit statue or wall you die. Just walk around. I have done
it half a dozen times and no problem. In free play, this area seems smaller and things
speed up a little. Story mode was slower. This was easier and simpler then 2 player mode
and trying to guess what character i.e. Fang or whatever to use. People tend to make this
overly hard to over think things.

This is probably the hardest crest to get in the whole game. There are some tips that you
can follow to make it a little easier though. You will need to get this crest when you are
running away from the dementors, after leaving the court room. You will run down a fairly
long corridor and eventually, you will run through a circular part of the corridor. In
this part, there is a statue and the crest is tucked behind it. You have to run round the
statue and grab it before the dementors catch up to you, or you will be sent straight to
the end and will have missed your chance to get it. This means you have to repeat the
level and try again. The two tips i will give you are these. Use fang, because he can run
slightly faster than other characters within the game. While duelling in the court room,
try to make sure the other character is set to fang. Then you can switch to him when he
starts to run ahead. I would also recommend that you run left as soon as you enter the
circular area, and go round the back of the statue, rather than trying to loop round the
front. I have done this three times and used these tips on the second two attempts. Both
times, they have never failed.