EDIT MAR 26 11:58 PM: My even-newer-than-what-was-previously-the-newest Courier (version 3.5, like the one true edition of D&D) is now here in Blue. Ignore the rest of this OP, for it's not that relevant anymore. See my latest post for comments.
EDIT NOV 12 4:59 PM: All text from the first edit which is now irrelevent will be now struck-through. See my absolute newest post for the reasoning behind Courier 3.0
EDIT OCT 31 12:50 AM: All old and irrelevant text now hidden by spoiler bars. See my newest post for more info, but please read the edits to this post as well!
Courier $6 (Even Newer!)
(Action)
+1 Card
+1 Action
You may reveal 1 Action or Treasure from your hand. If you do, gain any card costing no more $ than it does, and place both cards at the bottom of your deck.
***
I'm putting together the beginnings of an expansion which focuses upon future draws and shuffle/discard/deck interactions. This is the weirdest card I have so far a much more transparent card now, yay! and it's a bit difficult to analyze, so I turn to you But I'd still like your input.
Courier $6 [Newest!]
(Action)
+1 Card
+1 Action
You may reveal 1 Action or Treasure from your hand. If you do, gain any card costing less than it and place both cards at the bottom of your deck.
***
Courier $4 (New!)
(Action)
+1 action
At the start of your buy phase, gain a card costing less than the action you have in play which costs the most coins. Place the gained card at the bottom of your deck.
***
Old Courier $4
(Action)
+1 action
At the end of your action phase, gain a card costing less than the action you have in play which costs the most coins. After you gain that card, if your deck or your discard pile has two or fewer cards, you may put the gained card on top of your deck.
***
I've gone through the various scenarios involved in a (New) Courier opening, and found that if it hasn't been drawn or revealed dead in turn 3, it will give you an extra $3 card that you are guaranteed to see in turn 5, along with 2-4 cards from the reshuffle. Of course, improbable interactions with Loan or opponents' attacks might possibly make the gained $3 card available turn 4, or even delay it to turn 6, but worrying about that's like worrying about the opponent(s) poorly timing Noble Brigand or Fortune Teller, or the occasional 5-2 split in a Mountebank game.
However, if you open Chancellor-Courier, and turn 3 draw both Chancellor and Courier, you could see your extra $3 card with 4 cards of the reshuffle on turn 4. A neat little improbable trick that shouldn't break the game, because even if you get gold, you're at the beginning of a fresh draw and will still have to wait.
Since $5 actions are usually the most powerful ones you play, this amounts to an ironworks-ish effect, and $3-4 cards are usually not ones you want to accumulate too many of. At the same time, this card will increase in strength when you start playing $5, $6, or $7 actions. And when you approach the dreaded reshuffle of a heavily-greened deck in the late game, if you have been playing this card, it will reinforce your first hand so that you can hopefully maintain your momentum. And if you've built such a powerful engine that you're drawing your whole hand each turn... Well, you're probably already doing well for yourself, so it hopefully isn't too broken.
Random notes:
A) This card makes it important to note when your deck has 0 cards... Technically you only reshuffle when there's 0 cards left and you need to draw more, but people IRL might take a shortcut and reshuffle when they reach exactly 0... Might be a problem...
B) I worded this card to be clear about interactions with potion costs. You can't gain any potion-costing cards if your most coins-costing card the card you put back didn't cost a potion as well. But if you played put back a Golem (and no actions costing $5 or more), you can gain an Alchemist. And if you played put back even a Scrying Pool, you can gain a Vineyards(!)...
C) Chancellor FTW!