Card interactions of Card B:
Played by opponent:
Bureaucrat (makes you lose CB if you revealed it, loses track)
Spy (makes you lose CB if revealed, loses track)
Thief (same, can't steal it as it isn't trashed and Thief mentions "trashed cards")
Saboteur (makes you lose all Card Bs it hits before the first 3$+, loses track)
Tribute (makes you lose CB but gets a nice bonus for revealing it, loses track. Two CBs are revealed cards with the same name.)
Cutpurse (if you reveal your hand, all CBs are gone)
Pirate Ship (removes CB, loses track of it and produces no coin tokens for them as it only cares about trashed cards)
Rabble (removes all CBs it hits, loses track)
Fortune Teller (removes CB and stops there as CB is a Victory Card, loses track)
Oracle (removes, loses track)
Noble Brigand (removes CB, but counts it as a revealed Tresure, loses track)
Knights (remove CB, loses track)
Rogue (removes CB, loses track)
For most top-deck attacks it turns out CB keeps them from putting annoying VP cards on your deck, but at the downside, you lose a nice 1 VP card/Silver. Some attacks get a bit stronger, some a bit weaker. Saboteur, Tribute and Cutpurse are the big winners here, but Bureaucrat, Spy and Noble Brigand also don't mind it.
Played by yourself:
Adventurer (makes you lose your CBs, but counts them as revealed Treasures. If you reveal two Card Bs, both are removed and you put no card in your hand as they are lost track of. Becomes awful.)
Shanty Town (makes you lose CB)
Wishing Well (makes you lose CB, loses track)
Scout (becomes even more terrible, loses track)
Ambassador (you may reveal CB and return it to the pile, but can't return other ones as CB is not in the supply. No one gains CB.)
Apothecary (removes CB, loses track)
Golem (removes Card Bs it hits, loses track, bad.)
Scrying Pool (removes opponents CBs and your own. Counts as a revealed card that is not an action and stops the reveal-chain. You don't put it in your hand and opponents don't discard/top-deck it as it's lost track of)
Loan (removes CB, but stops when it's revealed. You can't trash or discard it as it's lost track of, also pretty bad.)
Mint (You may reveal CB, which makes you lose it. You can't gain a copy as it's not in the supply)
Venture (stops as CB is revealed. CB can't be played as it's lost track of, awful)
Farming Village (removes CB if it hits it, stops there and loses track so you don't get it in hand)
Harvest (removes CBs but counts them for bonus, loses track)
Crossroads (removes CB but counts it, loses track)
Vagrant (removes CB, loses track)
Sage (removes CB when hit, loses track)
Ironmonger (removes Cb, but counts it and gets the bonus, loses track)
Wandring Minstrel (removes CB, loses track)
Rebuild (Removes CB. If CB is not the named card, you gain a card costing up to 3$ without trashing CB - see eHalcyons statements for this)
Mystic (removes CB, loses track)
Doctor (removes CB, loses track)
Herald (removes CB, loses track)
Journeyman (removes CBs but counts them, loses track)
Most of those cards get much worse when you play them in your Card-B-kingdom. Scrying Pool is even worse for you than for your opponents, assuming about the same deck. Adventurer, Venture, Golem, Farming Village, Apothecary, Scout and Loan also don't like Card B a bit.
Interesting:
Possession (no direct interaction, but allows nasty things like Rebuild with "Card B" said to remove all of them from your deck. Such shenanigans require the opponent to go for Card B in the first place, as said before.)
Menagerie (as you reveal your hand, all CBs leave. If CB was the only card you had multiple of, you draw 3 cards, as Menagerie doesn't care about the cards revealed, but the cards "in your hand". I admit this one's a bit tougher...)
Hunting Party (Tough, like Menagerie. If you have CB in hand, it gets removed as you reveal it. If you then reveal CB from your deck, it isn't "a duplicate of one in your hand" and so Hunting Party stops to reveal cards. You don't put it in your hand, though, as it returns to its pile. Hunting Party is awful with Card B...)
Pillage (counts the size of your hand before reveal. If, by revealing your cards, you lose CBs, the opponent still picks one to discard. One might argue if the Pillager might chose a revealed CB.)
Envoy (removes CB when it's revealed. As with Pillage the opponent still picks one of the remaining cards. You might even argue that "one of them" relates to the revealed cards and so he could chose a revealed Card B)