Thanks for the numerous submissions, despite my slightly repetitive challenge!
This was very difficult as there were so many great cards. Favourites are bolded.
Hypocrite by AquilaAlthough 'attacking everybody including yourself' is novel, it has a classical feel. A clean design and a clear favourite.
The Copper junking can be quite nasty when you play with few Treasures which is more likely in a Kingdom with trashers which again limits the nastiness of the Copper-junking.
What you obviously aim for is something like Village, Village, Hypocrite-Militia, Hypocrite-Copperjunker, trash your Coppers. Seems near impossible in 2P but in 3P that double Attack can be smeared over 2 turns: Alice plays Hypocrite-Militia, Bob plays some draw and then Hypocrite-Copperjunker, Charlie will suffer.
Bellwether by pubbyCool idea but unsound implementation.
This is either a Copper/Curse junker, a Woodcutter Estate junker or a payload card that gains cards for the opponents.
All junking options are relatively weak (and come with the additional problem that you lack control as an opponent makes the choice) while the gaining option is nearly as good for the opponents as for you (unless you managed to play all your Actions, then e.g. gaining a Silver is relatively weak compared to +3 +1 Buy).
The main issue is that once you green, Bellwether becomes unplayable (so why did you buy it in the first place instead of Woodcutter?). This could be fixed via reducing the upper limit of Coin generation while creating the new problem of Province rushing (Alice play Bellwether, Bob reveals Province, Bob and Charlie gain a Province, Alice uses the 8 Coins and the Buy to buy a Province).
Consulate by King LeonPerhaps I am missing something but this looks too weak.
Suppose you gain a Curse to hand and are able to trash it during the same turn. Then this is better than Sea Hag (one more Coin).
Suppose you gain a Curse to hand and are unable to trash it during the same turn. Then this is worse than Fortune Teller (one less Coin).
Suppose you gain a Copper to hand and don't trash it. Then this is like a terminal Silver that comes with a downside for everybody.
Gaining $3s to hand seems OK but not that brilliant (unless you are able to pull off tricks familar from Messenger like Humble Castle).
Making the card a terminal Silver would be one way to potentially fix it.
Arson/Damages by Commodore ChucklesWe know the downgrading idea from Saboteur and Swindler and this looks like a fun combination of a trashing/junking attack. A definite favourite.
At 4 this looks at the first glance pretty strong. But if you open with this, at first play Arson is nearly always worse than Swindler: If you hit Copper, they gain a Ruins instead of a Curse and if you hit Estate, they get something better instead of another Estate.
I like that the Damages are not random such that you can pick whatever weakish engine piece you need. You can even imagine a Kingdom without any extra Buys in which you don't mind the first Arson hits that gift you Damaged Workshops.
The power level varies: Damaged Laboratory looks pretty strong whereas Damaged Estates is weak (but in a Shepherd game ...). But as you can always choose, this is no issue.
Corrosion/Tarnished by mail-miThe variability of the Curse substitutes is too low for my taste but the flexibility of the design (you could e.g. play with them in Kingdoms without Corrosion to nerf Cursers slightly) is neat.
I don't have much too say, this is simply a good design. The Tarnished cards are on average slightly nerfed Curses and Corrosion is sound. On a sidenote, for practical reasons I'd make Corrosion a Reserve card (although 4 types are always visually crammed). A card on the Tavern mat is easier to track than a card in set-aside-nirvana.
Red Tide/Barnacle by NoMoreFunThis is a great implementation of the 'block pile' idea but Red Tide is a bit too weak.
What can I say, Barnacle is just lovely. It is clean and you immediately get it (gotta pay $1 more, get a junk card that you can get rid off).
But Red Tide is probably too weak. Armory is not the greatest gainer, you'd rather have Ironworks or Devil's Workshop, and the other two $5 Workshop variants, i.e. Cobbler and Sculptor, always gain to hand. The pile-blocking can of course be used strategically, e.g. if you know that the opponent(s) are in dire need of a village, but it can also be neutral if they don't buy Barnacle and gain what they need via Red Tide.
Brazen Bull by FragasnapWeird card with a negative self-synergy.
So it a Treasure-Curser that you can defend against via playing an engine.
Power-level seems roughly OK but in the opening and early middlegame it will often hit and being nonterminal is pretty strong.
A 5/2 opening is likely even more game-deciding than Mountebank whose "defense option" is likely easier to trigger.
Curse being a dead card matters usually more than negative VPs and while I like the variable, negative VPs, I am no fan of the quick, early, non-terminal cursing.
Gremlin by faustA beautiful design with a potential nice nice minigame in non-mirrors about making a crucial engine piece a self-Hexer.
I love above all that this card creates new junk via just one token (instead of 30 new cards) and that, depending on what $2 card is Jinxed, play will vary a lot over Kingdoms (which isn't something one can say about all junkers).
Some folks who commented minded the Hexaganza but hey, nobody forces you to play 7 Hamlets in a row. That's the point of the card. If the Jinxed card is a cantrip, will you really play every card? Tricky decision.
Totem by GubumpAn interesting shot at a card with a very unusual cursing condition that suffers from making the 'deflect the attack' type of issue that is a big no for Reaction cards.
If Totem is in the Kingdom, nobody would ever gain another Curser. So all this does is to convert gainers or +1 Buy into cursing.
The economy is pretty strong, even if Totem misses a shuffle. But one has to keep in mind that this becomes dead once the Cursers are out.
I preferred the first version that always curses yourself, even though that suffered from being too scripted (in a 2P game, gain 2 Totems, first is a Cursed Gold, if Curses are distributed symmetrically you will play them a total of 7 times).
Plague Doctor/Plague by kru5hSoothsayer and Patron had a love child.
This looks pretty strong. Sure, nobody loves Silver but the hand-gaining can be nearly as good as Soothsayer's Gold while the opponent doesn't draw a card but can be rather junked again.
I like that the Silvers act as defense against Plague Doctor but like Soothsayer, the Treasure gaining can hurt strategically.
Diplomatic Gift by anordinarymanA very clean design that magically pulls off junkifying Silver, trashing and (quasi-)junking.
Charlatan by naitchmanA straightforward Swindler-Militia mixture.
Now you got a reason to stick with those Estates. After Charlatan has hit often enough and the Estate pile is empty, you might find Hamlets and can unleash the blue dogs from your former home.
This looks sound and it reduces the randomness of Swindler. But I think that in 2P games (in 3P games, chances are higher that a second Charlatan is played such that one opponent is down to 3) I'd more often than not prefer Swindler or Militia over this.
Lancers by KudasaiA balanced cantrip junker (already a bit of a design miracle to pull that off) that requires precise or non-mirror play to defend against.
The obvious question is whether this is good enough in a non-mirror. On the one hand, nonterminal draw for less than $5 is always in high demand. On the other hand, a semi-Lab for $4 is a bit weaker than Caravan.
But there is also a meta/strategy benefit if the opponents forsake Lancers: you are safe from the junking attack and can play Lancers more freely, i.e. without worrying about whether the Journey token is up or not.
Basically this card has these two built-in defenses: don't get Lancers and be safe, or get enough Lancers to make the Journey token be up more often. This implies sometimes having to decide to not play the last Lancer in hand and this very agonizing decision looks very appealing to me.
Metamorphosis by spinefluThis is too Kingdom-dependent, on average too weak and the on-buy junking is borderline pointless. It is a challenge about junking so that junking should be slightly more central.
Without Potion cards the only constructive thing this does is to convert Curses/Ruins into Coppers and Estates into stuff like blue dogs.
Suppose it is an Alchemist Kingdom. You'd rather buy Alchemist immediately instead of a stop card that can remodel Silvers into Alchemists.
Suppose it is a Scrying Pool Kingdom. Then being able to Remodel those Estates into Scrying Pools is quite sweet.
Suppose it is a Vineyard Kingdom. Then you definitely want this and you'll get the Potion earlier than you would otherwise.
This is no Counting House, this is no subtle card that require skill to find combos in which it works. It rather advertises bluntly that it is only good with one of the 4 cheap Potion cards.
Stockpile by scolapastaSelf-cursing to nerf a card wasn't the idea of the challenge but this is a great implementation of a "reloadable" Gold.
In my opinion the latest version is the best. The second version does on average yield as much as Silver while gaining a Curse at third play. This seems pretty bad but averages aren't everything; if you open Stockpile you have a near fail-safe chance (Stockpile,Copper,Estate,Estate,Estate) to hit $5 after the first shuffle.
And the third version comes with a pyramid-scheme like reloading which we know from Lackeys.
Shyster by mandioca15While the first version was broken, this can easily be too weak. Early on your will reveal Estates but e.g. in a mirror engine you got the best chances to hit if you reveal a village. But as Shyster doesn't draw, you want to play it last.
Racketeer by GazbagA Workshop-Curser, simple and good.
Playing with 2 Racketeers has a high opportunity cost and gainers always partially substitute extra Buys. But I nonetheless think that this might often enough Curse twice per turn.
That's why I'd consider making it a Copper junker. If it is too weak one can exchange the lines, such that this is basically guaranteed to junk 2 Coppers. That could be too strong though.
So yeah, the card already has a classical feel and I think that after some playtesting and perhaps some twitching it will become (or will turn out to already be) balanced and fun.
Scarab by majiponiThis is simply bad. There is a reason Magpies and Rats are cantrips.
You will sometimes keep your Necro and you can build a draw engine with Squire and Villa. But Squire+Smithy is like Peddler+Lab whereas Scarab+Smithy is just a Lab. In other words, villages that don't draw need a little extra to become decent.
You could argue that the "animal-style-procreation" thingy suffices as little extra but I have serious doubts. In a 2P games, Bob could simply not play along and those 10 Scarabs will hurt Alice far earlier and harsher than those 10 Curses will hurt Bob.
Runner-up: Lancers by KudasaiWinner: Gremlin by faustPS: I don't know whether it is mere coincidence but both of these cards imply having to make agonizing decisions. That's not always the case in Dominion, the focus is often more on what to gain than what to play.
