Haven't used any yet.
Do they have a point cost?
Can you use them repeatedly?
can you use more than one at a time?

No.
No. In a tournament, you may only use each card once.
No. In a tournament, you may only use one card per round.
(Not asked, but: you only bring a number of BFC cards equal to the number of the rounds of the tournament MINUS ONE, and use another card as a place holder in your "hand" of cards.)

Any of these answers can change with house rules...

I thought that the BFC were drawn randomly from you 'hand'. Orginally.

But after seeing the cards {double sided} and reading some more. I guess you choose which card you want for your round.

2 querries.

Since this is the case...Why the reason for the placecard?? It seems moot!??

You are supposed to have time to 'inspect' your opponents figures to make sure they are legal.
I have yet to see an official rule {or did I} about when you choose AND reveal your BFC for that round. Maybe you only brought 1 for the tourney anyhows.

Do you reveal it with your force before inspection?
Or do you get to reveal it after that after you can guess what your opponent may be playing?

thanks
wes

I got kicked around in a few game by BCF cards. Their are shown right when play starts. Which is why it is great to use Crosswind because if your opponent uses EarthQuake he takes damage too.