Sell cards now or wait for sale?

Mysterious Card will be dropping in price during sale.

I sold them... on sale they will start becoming very common.

How do you get these mysterious cards? Do you just craft badges?

Sell them now or by Wednesday at the latest. Historical trends say that they will likely be going down.

They might be higher at some point between now and the start of the sale, but after the first day, even during the first day the price tends to start dropping rapidly. You might be able to make a tiny bit of extra profit if you watch the market carefully, but you're probably better off selling them now rather than later.

I'm afraid there isn't room for two max's in this town, buddy.

I sold my 250 mysterious cards today.
I can already see the prices falling. Yes, it might go up for a very short period, but on the whole it will go downhill.