As I did with the 2s, I'll rework the 3s based on official wording, then give my thoughts on each card.
DEFLECTION
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+$2
Name a card type. Each other player discards a card of the named type from his hand (or reveals a hand with no cards of the named type), then draws a card.
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Action/Attack - $3
(Quite similar to you $2 card Assassin, but with more money, slightly less-perfect aim, and only one card drawn by opponents. I assume that the other players get to draw a card no matter what, including using Moat/Lighthouse. I see this as being more fun than Assassin as well -- name Attack, and if you whiff, your opponent might just draw that Attack you were trying to get rid of. Whoops!)
MERCENARY
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+$1
Each other player may discard a Treasure card from his hand. If he doesn't, he gains a Curse.
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Action/Attack - $3
(Worded this to feel more like Mountebank, since this is like Monty-lite. Terminal Copper instead of Silver, Coppers block it, and opponents don't get Coppers. The card creation guide advised against $3 Cursors, but the bribery defense mechanic makes this acceptable, in my opinion.)
RAGE
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+1 Buy
+$2
Discard a card.
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Whenever you discard a card from your hand, you may discard this from your hand. If you do, +2 Cards.
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Action/Reaction - $3
(A strictly-worse version of Woodcutter on its own, this could get pretty interesting if you have some Villages and enough Rages to combo with. Also good against cards like Cutpurse and your Mercenary, which can restore your hand size to 5, or Militia and Torturer, allowing you a net loss of just one card.)
RECYCLE
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Trash up to 2 cards from your hand. +1 Card per card trashed.
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If you trash a card, you may discard this card from your hand. If you do, gain a Silver.
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Action/Reaction - $3
(I'm guessing you want the reaction ability to work with all trashing, not just from your hand. If so, this would be interesting in Thief/Pirate Ship games for sure, because you can replace a trashed Copper with a Silver, but then you'll be potentially allowing your opponents to knock out said Silver. I want to try this out.)
EXPERIENCE
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$2
When you play this, gain a Treasure card costing up to $1 per Copper you have in play.
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When another players plays an Attack card, you may discard this from your hand. If you do, gain a copy of the Attack card played.
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Treasure/Reaction - $3
(So unless you have at least 3 Coppers in play, you'll be gaining a Copper when you play this. Most of the time, that might not make this card worth the purchase, but I could see this working magic along with Counting House. Of course, the Reaction might be the big draw if there are good stacking Actions on the board.)
SILVERSMITH
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+1 Buy
Silver produces an extra $2 this turn.
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Action - $3
(Build a good Silver engine, win the game easily. I agree with a lot of people in thinking that this is too strong as it is now.)
FIEFDOM
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When you play this, it's worth $1 for every Victory card you have in play (including this).
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1 VP
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Treasure/Victory - $3
(Certainly ridiculous when paired with Great Hall, Nobles, and/or Harem, and also has bonus power with Ironworks and Transmute (and Tribute), but by itself will probably just be cute. Worth trying, for sure.)
FOOT SOLDIER
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+$2
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1 VP
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Treasure/Victory - $3
(More reliable than Fiefdom, but nowhere near as much fun as a result.)
CASTLE
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Choose one: Set aside a Victory card from your hand onto your Castle mat (or reveal a hand with no Victory cards); or +$1 for each card on your Castle mat, then put a card from your Castle mat into your hand. Return all cards on your Castle mat to your deck at the end of the game.
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Action - $3
(Had to add a few things to clarify matters, I hope. If these clarifications are not what you had intended, let me know. As for my opinions, it's a bit like a self-imposed Pirate Ship/Island combo, but not quite as good as either. I might see this as a $4 myself)
PROSPECTOR
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+1 Card
+1 Action
Reveal the top 5 cards of your deck. Discard one of the revealed cards, then put the rest back on top of your deck in any order.
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Action - $3
(Yeah, this is better than Scout. Even if it doesn't automatically clean out the Victory cards, it's still far too easy to chain Prospectors together for a dominant deck. Dropping the revealed card amount to 3 might be for the best.)
FORMATION
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Whenever a player (including you) buys a card, you may discard this from your hand. If you do, gain a card costing up to $2 less than the card bought.
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Reaction - $3
(At last, a pure Reaction that I could see really working, since every game will have people buying cards. As WanderingWinder said, you could use this to nab a Duchy as the last Province is bought, hopefully giving you the win as a result. That does beg the question, what if multiple players reveal Formation, and they all want the same card, but there are not enough copies of the card to go around? Who gets priority? Would it be the player to the left of the card buyer?)