I'm not sure what the correct number of cars would be. I think 2 or 3 is correct.

Interesting. I like the phrasing that allows it to be good either on an opponent or on yourself. Reminiscent of Monomania. I fear even at 3 cards this will often be Fugue but cheaper, which sounds pretty backbreaking.

Mmm.. getting this on turn 3 or 2 and forcing a discard down to 3 is pretty harsh. Still Hymn to Tourach is nearly to as bad; and this lets you choose which to keep.... Maybe upcost by one? You don't want to keep too many, because on yourself this is card draw.

And, amusingly, it's a very very funny way to dodge card-discarders. Exile cards until you need them, then exile them back.