If you don't believe in yourself, nobody will!
You've gotten this far over hundreds of applicants. You ARE special, and you're going to ace this. It's normal to undervalue yourself, but remember that if anyone can get you through this AC, it's you. I used to work with the crypto industry, and a moniker there was:
'Make it easy for them to hire you.'
Make it easy for them.
So I see three things:
1) Negotiation exercise - check out
@Jacob Miller's crazy
good resources on being successful at negotiation here.
2) Case study - again, Jacob beat all of us to it.
See it here.
3) Presentation - is it a spontaneous presentation or a prepared one? I know anonymity is important for you but if you mention the firm some people might have experiences with the AC that they're willing to share! Alternatively, you can search around the forum using the 'search' function to look for people who've done the AC, and then private message them. Look at yourself in the mirror and practice your speaking, and make sure you can convince yourself of your own confidence!
edit* if this is somehow for a firm that rhymes with LoFo,
this thread might be of some use.