Ok I'll explain the joke really bad card idea.
Oh hey, I heard that explaining jokes and really bad card ideas is a thing in this Forum. I wanna have a go at that.
Jack, master salvager
$4 Action
Trash any number of non-treasure cards from your hand.
Jack, master scavenger
$4 Action
Look at the top card of your deck. You may discard it. You may repeat this any number of times.
Jack, master minter
$4 Action
Gain any number of silvers.
Jack, master librarian
$4 Action
Draw cards until you have 5 cards in hand. Repeat this any number of times.
Obviously the theme is turning Jack of all Trades into four different "Jack, master of a single trade" by letting you do the effect any number of times.
Draw-to-x multiple times is the same as doing it once, hence Master Librarian's "Repeat this any number of times" is superfluousand since most card text isn't, this would probably lead to confusion and avoidable rules questions. But the foolish consistency that is the hobgoblin of little minds is excellent fun ^^. Also, on 5-card hands, Master Librarian = Ruined Library.
Master Minter is CRAZY swingy: whoever gets it on turn 3* plays the infinite Silver deck and single provinces every** turn starting turn 5. **Unless enough junk collides, in which case it's not in any of your other hands. *Actually it's p1 t3 > p2 t3 > p1 t4 > p2 t4, so it has a MASSIVE first player advantage as well. Good with: Feodum. Bad against: Militia.
Master Salvager is a little better at trashing estates than Salvager, but not a lot (Best case: Master Salvager is as good as a Steward for one turn only). It's a lot worse at being virtual money. Maybe it can trash multiple Ruins/Curses, but... meh? On the whole, what makes this card a bad idea is that it's extremely weak.
Master Scavenger, my favorite. Here's approximately what it does: "Put you deck in your discard pile. Look through your discard pile and shuffle any number of cards into your deck. Look through your discard pile; you may put a card from it on top of your deck." they way you get that effect is by discarding from the top of your deck until by chance all the cards you want to discard are at the top of your shuffle, all the shuffled-into-deck are at the bottom, and the topdecked card is topmost among those you want to keep (or you can stop after having discarded those you want to discard and not look at the card on top, hence the reworded topdecking is optional). Recall when I said "by chance"? It's going to take FOREVER for that to happen (or maybe ~n! shuffles); which means that if you're a decent human being you don't actually play this out, you just... meh, I dunno? Chancellor yourself without the money?
TL;DR: very meh card, unnecessary rules questions, extreme imbalance, effect resolution that's slow as molasses. All important ingredients in a well-designed game