Anyhow, those are my thoughts! I'll try get to the last 3 soon!
Thanks for all your excellent feedback! I've made a fair few changes in light of your suggestions, and a few more following some very basic testing.
1) Informer: prevented it from stacking, and removed the choices so as to speed it up. Strong early game attack that weakens later on.
Informer ($5 Action-Attack)
+1 Card
+1 Action
+$1
You may discard a card from your hand. Each other player with at least 4 cards in their hand reveals a card from their hand costing more than it (or reveals a hand with no such cards), and puts it on top of their deck.
2) Witch doctor: left as is.
3) Artwork: rewritten, since it's just too easy to empty 3 cheap piles, meaning that any scaling $4 cost version ended up being OP against a non-mirror strategy.
Artwork ($4 Victory)
At the end of the game, this is worth 1VP for each empty Supply pile.
4) Master Smithy: left as is for now. Early testing suggests it's not as strong as it seems, due to terminal collisions and the discarding of set-aside cards, meaning that when you play it a second time you often get cards you excluded the first time but no longer have in hand so can't exclude again.
5) Patent: left as is.
6) Pension: rewritten to use coffers as suggested.
Pension ($3 Action-Duration)
Trash a card from your hand. For every $ it cost, place a coffer on this card. At the start of the next and subsequent turns: take a coffer from the pile. (This card stays in play until there are no coffers left.)
7) Gaulish village: rewritten to be more thematic and harder to stack.
Gaulish village ($1+1P Action)
+1 Card
+2 Actions
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When you discard this from play, you may first discard from play a Potion or an Attack card. If you do, put this onto your deck.
Counsel: weakened third option as suggested (but left it in so you never regret playing this).
Counsel ($5 Action)
+1 Action
Reveal all the cards in your hand. The player to your left chooses one. Either: gain a copy of it; trash it, +1 Card; or discard it, +2 Cards.
9) Spring Clean: rephrase from 'discard' to 'put in your discard pile' (like the various deck discarded) so it doesn't trigger on-discard effects.
Spring Clean ($3 Action)
+$2
Name a card. Look through your deck, and put any number of occurences of the card in your discard pile. Shuffle your deck.
10) Transmogrify: rename to Metamorphosis.
11) Agent: totally rewritten. Was OP as written and encouraged an uninteresting rush. Replacement will almost certainly need tweaking, but I'm hopeful with the concept.
Forged Letter ($5 Treasure-Attack-Reaction-Duration)
If this is your turn: +1 Coffer & each other player discards down to 3 cards.
Otherwise: at the start of your next turn, +1 Coffer.
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When another player plays an Attack card, you may first pay a Coffer to play this from your hand. While this is in play, when another player plays an Attack card, you are not affected.
12) Home laboratory: left as is for now.
13) Chaplain: price increased to $4 partly to avoid a double Chaplain start.
14) Study: totally rewritten. Like Agent, I couldn't get this to work. Expect this'll need tweaking.
Warlock ($5 Action-Attack)
You may return a VP token. If you do, each other player gains a Curse. Otherwise, +1VP.
You may return a Coffer. If you do, each other player discards down to 3 cards. Otherwise, +1 Coffer.
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When you gain this, +1 VP.
15) Night shift: not sure what the original intent was, so made it sort of attacky (a $2 attack?!).
Night Shift ($2 Action-Duration)
Now and at the start of your next turn: +1 Coffer.
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While this is in play, cards cost $1 more for everyone (after any cost reductions).
16-18) Left as is until further testing.